perf: mark ReaderT context argument as borrow

[hargoniX]

This PR marks the context argument of ReaderT as borrowed, causing a wide spread of useful borrow annotations throughout the entire meta stack which reduces RC pressure. This introduces a crucial new behavior: When modifying ReaderT context, e.g. through withReader this will almost always cause an allocation. Given that the ReaderT context is frequently used in a non-linear fashion anyways we think this is an acceptable behavior.

[mathlib-lean-pr-testing]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 133fd016b4ed1f0108945ce2f1a1b7ffbb3f6575 --onto 6714601ee4a123fef0f6ff3e44f01086ba78dfce. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-17 12:02:09)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 4ba85acc464e380c03034763e93506f695ae68d7 --onto 6714601ee4a123fef0f6ff3e44f01086ba78dfce. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-17 21:02:47)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 091726034110408555f0bca58cfebbf39b524147 --onto 61a3443a9569d548a235f785b9a33984bb7ff622. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-18 10:53:14)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 4d6accd55d4ec6997b2a247bce3ecf811beb4c8e --onto 87180a09c49c91577e54284703c73c5ca76be126. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-20 18:39:12)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 4a62d4a79be4298c8738c8bee94f9d325230ad79 --onto 87180a09c49c91577e54284703c73c5ca76be126. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-21 06:02:49)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 133fd016b4ed1f0108945ce2f1a1b7ffbb3f6575 --onto cfa8c5a036d6990635c6ec50b02d0e806995cec3. You can force reference manual CI using the force-manual-ci label. (2026-03-17 12:02:10)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 4ba85acc464e380c03034763e93506f695ae68d7 --onto cfa8c5a036d6990635c6ec50b02d0e806995cec3. You can force reference manual CI using the force-manual-ci label. (2026-03-17 21:02:48)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 091726034110408555f0bca58cfebbf39b524147 --onto cfa8c5a036d6990635c6ec50b02d0e806995cec3. You can force reference manual CI using the force-manual-ci label. (2026-03-18 10:53:15)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 4d6accd55d4ec6997b2a247bce3ecf811beb4c8e --onto cfa8c5a036d6990635c6ec50b02d0e806995cec3. You can force reference manual CI using the force-manual-ci label. (2026-03-20 18:39:14)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 4a62d4a79be4298c8738c8bee94f9d325230ad79 --onto cfa8c5a036d6990635c6ec50b02d0e806995cec3. You can force reference manual CI using the force-manual-ci label. (2026-03-21 06:02:50)

[hargoniX]

!bench

[leanprover-radar]

Benchmark results for 1fdf271 against 511be30 are in. Significant changes detected! @hargoniX

• ✅ build//instructions: -165.4G (-1.35%)
• 🟥 other exited with code -1

Large changes (4✅)

• ✅ size/all/.c//lines: -189.9k (-1.70%)
• ✅ size/all/.ir//bytes: -8MiB (-2.54%)
• ✅ size/install//bytes: -26MiB (-1.05%)
• ✅ size/libleanshared.so//bytes: -7MiB (-5.22%)

Medium changes (15✅)

• ✅ build//instructions: -165.4G (-1.35%)
• ✅ build/module/Init.Data.BitVec.Lemmas//instructions: -1.6G (-1.18%)
• ✅ build/module/Init.Data.Nat.Linear//instructions: -4.5G (-7.28%)
• ✅ build/module/Init.Data.Nat.SOM//instructions: -2.1G (-9.57%) (reduced significance based on absolute threshold)
• ✅ build/module/Lake.CLI.Main//instructions: -1.2G (-3.25%) (reduced significance based on absolute threshold)
• ✅ build/module/Lean.Elab.Do.Legacy//instructions: -1.1G (-2.05%) (reduced significance based on absolute threshold)
• ✅ build/module/Lean.Elab.DocString.Builtin//instructions: -1.1G (-2.16%) (reduced significance based on absolute threshold)
• ✅ build/module/Lean.Meta.Tactic.FunInd//instructions: -1.2G (-1.93%)
• ✅ build/module/Lean.Meta.Tactic.Grind.Arith.CommRing.EqCnstr//instructions: -1.0G (-2.12%)
• ✅ build/module/Lean.Meta.Tactic.Grind.EMatch//instructions: -1.3G (-1.84%) (reduced significance based on absolute threshold)
• ✅ build/module/Std.Data.DHashMap.RawLemmas//instructions: -1.4G (-0.89%)
• ✅ build/module/Std.Data.DTreeMap.Internal.Lemmas//instructions: -3.3G (-1.53%) (reduced significance based on absolute threshold)
• ✅ build/module/Std.Data.Internal.List.Associative//instructions: -1.2G (-1.40%)
• ✅ build/module/Std.Tactic.BVDecide.Bitblast.BVExpr.Circuit.Lemmas.Expr//instructions: -2.2G (-1.88%) (reduced significance based on absolute threshold)
• ✅ build/module/Std.Tactic.BVDecide.LRAT.Internal.Formula.RupAddResult//instructions: -1.1G (-2.07%) (reduced significance based on absolute threshold)

and 1 hidden

Small changes (1201✅)

Too many entries to display here. View the full report on radar instead.

[hargoniX]

!bench

[leanprover-radar]

Benchmark results for d34f8f2 against 4a62d4a are in. Significant changes detected! @hargoniX

• ✅ build//instructions: -150.0G (-1.22%)

Large changes (9✅)

• ✅ elab/big_do//instructions: -597.8M (-2.44%)
• ✅ elab/grind_bitvec2//instructions: -3.3G (-1.66%)
• ✅ elab/grind_list2//instructions: -1.0G (-1.87%)
• ✅ elab/simp_local//instructions: -1.7G (-3.78%)
• ✅ size/all/.c//lines: -238.0k (-2.12%)
• ✅ size/all/.ir//bytes: -9MiB (-2.78%)
• ✅ size/compile/.out//bytes: -183MiB (-9.52%)
• ✅ size/install//bytes: -27MiB (-1.11%)
• ✅ size/libleanshared.so//bytes: -8MiB (-5.46%)

Medium changes (29✅)

Too many entries to display here. View the full report on radar instead.

Small changes (1118✅, 6🟥)

Too many entries to display here. View the full report on radar instead.