feat(test-cli): add JSON output and optimization analysis to groupstats

[danceratopz]

Description

Improve the groupstats pre-allocation group analysis utility so it is useful for both human inspection and programmatic/agent-driven analysis.

The command now supports:

• --output rich|json to switch between the existing rich console view and machine-readable JSON.
• --low-test-count to define which groups should be treated as optimization targets.
• --limit to bound candidate result lists, with 0 meaning no limit.
• --include-test-ids to opt into full test ID lists.
• --include-group-details/--exclude-group-details to control per-group output size.
• --compact to omit verbose top-level maps while keeping totals, distributions, fork stats, and optimization candidates.
• --match-test-id and --match-test-id-regex to focus analysis on matching tests before recomputing rich or JSON stats.
• --exclude-test-id and --exclude-test-id-regex to remove known-noisy tests before recomputing rich or JSON stats.

The command help now includes an agent/programmatic example and points callers at the JSON optimization object, especially candidate_buckets, as the first place to inspect for possible larger group opportunities.

The analyzer now reads pre-alloc group JSON directly into lightweight records instead of loading full fixture models, and reports ranked optimization data for:

• low-count groups,
• candidate buckets sharing fork, chain ID, group salt, and environment,
• test-function candidates,
• module candidates.

The rich output keeps the existing at-a-glance tables and adds singleton/low-count summaries plus a candidate-bucket table.

Validated via:

• uv run pytest packages/testing/src/execution_testing/cli/tests/test_show_pre_alloc_group_stats.py
• just static
• uv run groupstats --help
• Manual validation against the cached tests%40v20.0.1 blockchain_tests_engine_x/pre_alloc fixture directory in both rich and JSON modes.

Related Issues or PRs

N/A.

Checklist

• Ran fast static checks to avoid CI fails, see Code Standards & Verifying Changes: just static
• PR title has the form <type>(<area>): <title>, where <type> and <area> come from an appropriate C-<type>, respectively A-<area>, label. The title should match the target squash commit message.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.49%. Comparing base (5bb2a51) to head (25c507b).

Additional details and impacted files

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  Hits                 34647    34647           
  Misses                1653     1653           
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unittests	93.49% <ø> (ø)

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