Auto-initialize git submodules in bundle target

[Copilot]

The make bundle command fails with No such file or directory when the z-core submodule containing zbundler.py is uninitialized in fresh clones.

Changes

• Modified bundle target to detect missing bundler script and auto-initialize submodules via git submodule update --init --recursive
• Zero overhead when submodule already exists

Behavior

# Previously required manual initialization
make init
make bundle

# Now works immediately on fresh clone
make bundle  # Auto-initializes submodules if needed

All targets depending on bundle (bench_c, bench_optimized, lua, etc.) now work without manual intervention.

Original prompt

please can you fix following error make USE_MIMALLOC=1 bench_optimized
Bundling zstr.h...
python3 z-core/zbundler.py src/zstr.c zstr.h
/usr/lib/python-exec/python3.13/python3: can't open file '/tmp/test/zstr.h/z-core/zbundler.py': [Errno 2] No such file or directory
make: *** [Makefile:84: bundle] Error 2

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[Copilot]

Pull request overview

This PR adds automatic git submodule initialization to the bundle target, eliminating the need for users to manually run make init before building. The change detects when the bundler script is missing and automatically initializes submodules.

• Adds conditional check for missing zbundler.py script before bundle execution
• Auto-initializes git submodules when the bundler script is not found
• Removes manual initialization step from the workflow for fresh repository clones

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[Copilot]

The git submodule update --init --recursive command could fail (e.g., network issues, invalid git repository), but this failure would not stop the make process. The subsequent python3 $(BUNDLER) command would still execute and fail with a confusing error message.

Consider adding error handling by appending || exit 1 to the git command:

@if [ ! -f $(BUNDLER) ]; then \
	echo "Initializing git submodules..."; \
	git submodule update --init --recursive || exit 1; \
fi

This ensures the build fails immediately with a clear error if submodule initialization fails.

Suggested change

	git submodule update --init --recursive; \
	git submodule update --init --recursive || exit 1; \