ci: scope runner disk cleanup per job and trim rust pre-merge setup

[hubcio]

The rust coverage baseline ran instrumented cargo-llvm-cov builds that
exhausted the runner disk ("No space left on device" at ~34 MB free);
object sizes roughly double under instrumentation and the light cleanup
(~12 GiB) left too little headroom. Add an opt-in aggressive input to
the free-disk-space action that runs jlumbroso/free-disk-space (~30+ GiB,
already on the ASF actions allowlist) instead of the light removal,
threaded through setup-rust-with-cache and enabled only on the coverage
job. The .NET SDK is preserved when provisioned so dotnet jobs stay safe.

The inverse also holds. The light cleanup costs ~20-45s, but the runner
has ~89 GiB free before it runs, far more than any non-coverage rust leg
needs. Make disk cleanup opt-out per task and skip it on the light legs
(fmt, sort, clippy, check, machete, doctest); the disk-heavy legs
(test-*, compat, miri, verify-publish, cross-builds) keep it. Every other
caller keeps the light path through the default.

While in the rust pre-merge action, two further setup trims: install
cargo-sort and cargo-machete from taiki-e/install-action prebuilt
binaries instead of compiling them from source on every run (cargo-http-registry
stays a source build, no prebuilt exists), and drop a redundant second
apt-get update in the test legs, since setup-rust-with-cache already
refreshed the apt lists earlier in the same job.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.43%. Comparing base (5858410) to head (8aa35e9).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3406      +/-   ##
============================================
- Coverage     74.46%   74.43%   -0.03%     
  Complexity      943      943              
============================================
  Files          1231     1231              
  Lines        120911   120911              
  Branches      97648    97677      +29     
============================================
- Hits          90042    90006      -36     
+ Misses        27918    27913       -5     
- Partials       2951     2992      +41     

Components	Coverage Δ
Rust Core	75.61% <ø> (-0.01%)	⬇️
Java SDK	58.44% <ø> (ø)
C# SDK	69.41% <ø> (-0.55%)	⬇️
Python SDK	81.06% <ø> (ø)
Node SDK	91.53% <ø> (+0.01%)	⬆️
Go SDK	40.20% <ø> (ø)
see 30 files with indirect coverage changes

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