ci(rust): skip unnecessary setup steps

[Standing-Man]

Rationale

Rust CI was doing redundant work in two areas:

1. Lightweight checks such as formatting, dependency sorting, and
   cargo machete installed nextest and system dependencies that they
   did not use.
2. The two nextest partitions independently compiled the same
   coverage-instrumented workspace before running their respective test
   subsets.

This increased both CI setup time and total compute usage.

What changed?

• Added configurable Rust setup options for installing nextest and
  platform-specific system dependencies.
• Skipped unnecessary setup for formatting, sorting, and machete jobs.
• Explicitly enabled nextest only for jobs that require it.
• Replaced the two independently compiled Rust test tasks with:
  • one build job that determines the affected crates and creates a
    coverage-instrumented nextest archive;
  • two test jobs that download the same archive and execute separate
    hash partitions.
• Packaged connector shared libraries alongside the nextest archive so
  integration tests can continue to resolve runtime plugins.
• Preserved cargo-rail affected-crate filtering, nextest retries, runtime
  setup, and per-partition Codecov reports.
• Added a benchmark workflow for comparing the baseline and optimized
  Rust setup paths.
• Updated the Python interpreter synchronization script to use a
  portable Bash shebang.

Results

The setup optimization was measured over three runs:

Measurement	Baseline median	Optimized median	Improvement
Rust setup step	44 s	13 s	31 s / 70.5%
Benchmark job	52 s	20 s	32 s / 61.5%

A pre-merge comparison showed:

Job	Baseline	Optimized	Improvement
fmt	47 s	22 s	25 s / 53%
sort	42 s	19 s	23 s / 55%
machete	79 s	61 s	18 s / 23%
Combined	168 s	102 s	66 s / 39%

The benchmark link.

Local Execution

• Passed / not passed
  Passed
• Pre-commit hooks ran / not ran
  Ran

AI Usage

[github-actions]

Thanks for the PR. It is labeled S-waiting-on-review and queued for review.

Slash commands (own line, regular comment) move it around the queue:

• /ready - back to S-waiting-on-review after addressing feedback
• /author - flip to S-waiting-on-author while you finish changes
• /request-review @user-or-team - request a reviewer

See CONTRIBUTING.md for details.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.34%. Comparing base (d9635b6) to head (4526ce8).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3749      +/-   ##
============================================
- Coverage     74.53%   74.34%   -0.20%     
  Complexity      969      969              
============================================
  Files          1306     1306              
  Lines        150028   150028              
  Branches     125462   125534      +72     
============================================
- Hits         111829   111535     -294     
- Misses        34700    34909     +209     
- Partials       3499     3584      +85     

Components	Coverage Δ
Rust Core	74.66% <ø> (-0.18%)	⬇️
Java SDK	62.71% <ø> (ø)
C# SDK	71.13% <ø> (-1.14%)	⬇️
Python SDK	92.27% <ø> (ø)
PHP SDK	84.52% <ø> (ø)
Node SDK	92.20% <ø> (-0.05%)	⬇️
Go SDK	43.08% <ø> (ø)
see 50 files with indirect coverage changes

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