apollo_compilation_utils: resolve tools root next to the executable when present

[avi-starkware]

Why

Prebuilt binaries distributed outside Docker (e.g. a natively-built starknet_transaction_prover for macOS) cannot run Sierra→CASM compilation out of the box: binary_path() resolves the sidecar compiler under $CARGO_TOOLS_ROOT (default ~/.cargo/tools), which does not exist on a machine that never ran scripts/install_compiler_binaries.sh. The recipient currently must either install the toolchain and run the script, or know to set CARGO_TOOLS_ROOT manually — neither is documented for binary recipients. (Background: #14379 hit the harsher, unrecoverable variant of this on the privacy release line.)

What

cargo_tools_root() now checks for a tools directory next to the running executable, after the explicit $CARGO_TOOLS_ROOT override but before the cargo-home default. This makes a packaged layout work with zero configuration:

package/
├── starknet_transaction_prover
└── tools/
    └── starknet-sierra-compile-<version>/
        └── bin/starknet-sierra-compile

The tools/ subtree is exactly what scripts/install_compiler_binaries.sh --sierra produces under CARGO_TOOLS_ROOT, so a packaging job can stage it with:

CARGO_TOOLS_ROOT="$PKG_DIR/tools" scripts/install_compiler_binaries.sh --sierra

The version-suffixed directory layout and verify_compiler_binary() checks are unchanged, so a stale package still fails loudly with the exact expected path.

No behavior change for existing setups:

• Docker images set CARGO_TOOLS_ROOT explicitly (e.g. /opt/cargo-tools) — the env var branch still wins.
• Dev machines have no tools directory next to target/{debug,release} binaries — the is_dir() guard falls through to ~/.cargo/tools as before.

Validation

• cargo build -p apollo_compilation_utils — passes
• SEED=0 cargo test -p apollo_compilation_utils — 10 passed, 0 failed (includes 3 new tests for the exe-relative resolution)
• cargo clippy -p apollo_compilation_utils --all-targets — clean
• scripts/rust_fmt.sh — applied

🤖 Generated with Claude Code

[reviewable-StarkWare]

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