fix: bb format.sh re-staging inside worktrees

[nchamo]

Problem

.git/hooks/pre-commit runs barretenberg/cpp/format.sh staged, which lists staged C++ files with git diff-index --relative --cached and re-git adds them after clang-format. Git sets GIT_DIR to an absolute path when invoking hooks; inside a worktree that makes --relative resolve against the wrong root, so the re-add runs git add on a path that is in the index but does not exist at the expected location — which stages a deletion. Committing inside a worktree therefore silently drops staged .cpp/.hpp files from the tree. Hit in practice when a merge that touched 34 barretenberg C++ files committed them away.

Fix

unset GIT_DIR near the top of format.sh, so the relative paths resolve against the worktree root. Same bug and one-liner fix as #22557 (yarn-project/precommit.sh) and #23628 (noir-projects/precommit.sh); format.sh is the last pre-commit hook script that still had it.

[AztecBot]

Flakey Tests

🤖 says: This CI run detected 1 tests that failed, but were tolerated due to a .test_patterns.yml entry.

\033FLAKED\033 (8;;http://ci.aztec-labs.com/539408366d850f2c�539408366d850f2c8;;�):  yarn-project/end-to-end/scripts/run_test.sh simple src/e2e_slashing/attested_invalid_proposal.test.ts (461s) (code: 0)