Add lintrunner pre-commit hook

[abhinaykukkadapu]

Add lintrunner pre-commit hook

Summary:
Run lintrunner automatically on every commit via .githooks/pre-commit.
Hooks are enabled by default through install_executorch.sh.

Test Plan:

• lintrunner not installed: warns and skips
• .lintrunner.toml missing: warns and skips
• First init (no hash stored): runs lintrunner init, stores hash
• Second commit (toml unchanged): skips init
• .lintrunner.toml modified: re-runs init
• lintrunner init fails: blocks commit
• First commit (no HEAD^): runs without error
• Clean file: lint passes, commit succeeds
• Lint violation: lint fails, commit blocked
• sha256sum/shasum produce same hash

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18689

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 1 New Failure, 2 Unrelated Failures

As of commit 93af227 with merge base afc9989 ():

NEW FAILURE - The following job has failed:

• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[github-actions]

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