Add per-test configuration overrides

[MatthewMckee4]

Summary

Adds [[profile.<name>.overrides]] entries that pair a filter expression with one or more option fields. The first matching override wins for each test, falling back to the profile-level value when nothing matches.

[profile.default.test]
retry = 1
timeout = 30.0

[[profile.default.overrides]]
filter = "tag(network)"
retries = 5
timeout = 300.0

[[profile.default.overrides]]
filter = "tag(unit)"
retries = 0
slow-timeout = 0.5

The override entry currently supports retries, timeout, and slow-timeout, mirroring the equivalent profile-level fields. A matching override with a non-positive timeout or slow-timeout disables the corresponding limit for the matched test even when the profile sets one.

Filters use the existing filterset DSL (tag(...), test(...), and boolean combinators) and are validated at TOML parse time via a ValidatedFilter newtype, so the worker never re-parses or panics. Overrides defined under [profile.default] are layered beneath named-profile entries: a [[profile.ci.overrides]] block takes precedence when the ci profile is active, with default-profile entries as the fallback. Overrides are forwarded from the main process to workers via a hidden, JSON-encoded --override-json flag.

Closes #555. Closes #577.

Test Plan

ci

[codspeed-hq]

Merging this PR will improve performance by 10.06%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	WallTime	karva_benchmark	56.9 s	51.7 s	+10.06%

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_{Comparing worktree-nested-wandering-acorn (40c3e12) with main (eb3c800)}