ci: add affected-crate detection to skip unchanged tests

[Rani367]

Problem

This repo has 36 crates in its Cargo workspace. The current CI uses a custom matrices.py to partition tests, but it doesn't filter which crates need testing based on what changed.

I analyzed the last 15 commits on master:

Commit	Message	Affected	Total	Reduction
e2b2529	feat(evm): make Executor generic	9	36	75%
f4a6885	clippy: warn on redundant_else	25	36	31%
179b8f7	feat(evm): add Tempo precompile	29	36	19%

Example — an EVM change affects 9 of 36 crates with full dependency chains:

9 affected package(s) (base: HEAD~1, 1 files changed):

  ● foundry-evm      (directly changed)
  ● forge             (depends on: forge → foundry-evm)
  ● anvil             (depends on: anvil → foundry-evm)
  ● cast              (depends on: cast → foundry-evm)
  ...
  (27 crates NOT affected)

What this PR adds

• .affected.toml — config file (ignores docs/markdown/CI/testdata files)
• .github/workflows/affected-test.yml — experimental workflow that:
  1. Detects affected crates via affected ci
  2. Creates a dynamic GitHub Actions matrix
  3. Runs cargo nextest run -p <crate> per affected crate

This complements matrices.py by narrowing which crates enter the matrix, rather than partitioning all 36.

This runs alongside existing CI — it does NOT replace anything.

What affected is

affected — single 5MB Rust binary, zero config, MIT licensed. Auto-detects Cargo workspaces. Has a GitHub Action and PR comment bot.

[zerosnacks]

Thanks for your suggestion, I'll reconsider this but for now decided against it.

[Rani367]

No worries, thanks for considering it.