chore(audit): audit math expressions across Spark 3.4.3, 3.5.8, 4.0.1, 4.1.1

[andygrove]

Which issue does this PR close?

Closes #.

Rationale for this change

Continuation of the per-category expression audit. Same pattern as #4483 (array), #4480 (predicate), #4479 (bitwise), #4478 (map), #4476 (hash), #4475 (conditional), #4474 (misc), #4473 (collection), #4470 (json), #4469 (struct), using the updated audit-comet-expression skill in #4468.

What changes are included in this PR?

Support-doc audit notes

Add per-version audit sub-bullets to all 60 supported math SQL function names (%, *, +, -, /, abs, all trig and inverse-trig, all log/exp/pow/sqrt/cbrt, bin, hex, unhex, greatest, least, ceil/ceiling/floor/round/rint/sign/signum, div/mod/negative/positive/pi, try_add/try_divide/try_multiply/try_subtract, width_bucket). Add 4.1.1 audit line to the already-audited factorial. rand / randn cross-reference the misc audit (#4474); shiftleft cross-references the bitwise audit (#4479).

Highlights from the cross-version review:

• All trig and exp/log helpers are byte-for-byte stable across the four Spark versions; the only systemic change in 4.0 is the NullIntolerant trait -> nullIntolerant: Boolean field refactor.
• 4.0 also adds the DefaultStringProducingExpression trait on Bin / Hex / Unhex and widens their StringType inputs to StringTypeWithCollation.
• UnaryPositive becomes RuntimeReplaceable in 4.0; in 3.4/3.5 +col silently disables Comet for the enclosing projection because there is no CometUnaryPositive serde.
• CometRemainder rejects EvalMode.TRY, so try_mod on Spark 4.0+ falls back (filed as [Bug] try_mod falls back to Spark because CometRemainder rejects EvalMode.TRY #4484).
• Round falls back for Float / Double because BigDecimal-via-toString rounding cannot be precisely matched.
• width_bucket (Spark 3.5+) is wired via per-version CometExprShim rather than a CometExpressionSerde, bypassing the support-level framework (filed as [Bug] width_bucket bypasses CometExpressionSerde framework #4485).
• hex / unhex do not propagate Spark 4.x collation; covered by the umbrella [Spark 4.0] Add string collation support #2190.

Support-level consistency fixes

None in this PR. The audit surfaced several convert-time withInfo fallbacks in arithmetic.scala (CometAdd / CometSubtract / CometMultiply / CometDivide / CometIntegralDivide / CometRemainder / CometUnaryMinus / CometRound rely on the default Compatible(None) and bail out from convert for several cases). Lifting them into getSupportLevel / getUnsupportedReasons is mechanical but touches an unusually load-bearing file; deliberately deferred to follow-ups to keep this audit PR low-risk.

Tracking issues filed for follow-up

• [Bug] try_mod falls back to Spark because CometRemainder rejects EvalMode.TRY #4484 try_mod falls back to Spark because CometRemainder rejects EvalMode.TRY.
• [Bug] width_bucket bypasses CometExpressionSerde framework #4485 width_bucket bypasses the CometExpressionSerde framework.

Audit process

Audited using the audit-comet-expression skill (4 Spark versions per #4468), driven by 4 parallel agents covering arithmetic ops, trig + constants, log/exp/power/rounding, and misc (bin/hex/etc).

How are these changes tested?

• make core succeeds (no code changes; doc only).
• Existing test coverage in CometExpressionSuite, CometMathExpressionSuite, CometSqlFileTestSuite expressions/math/, and expressions/string/{hex,unhex}.sql remains unchanged.