Add YAML Mach-O parser fixtures

[MikeMcQuaid]

• Cover malformed command sizes, bounds and string offsets.
• Exercise byte order, build metadata and runtime paths.

Fixes #201

[Copilot]

Pull request overview

This PR expands the Mach-O parser’s resilience and test coverage by adding yaml2obj-generated fixtures and corresponding tests for malformed load command sizing/bounds and malformed lc_str offsets, plus a few sanity-check “known good” fixture cases (endianness, build metadata, rpaths).

Changes:

• Add parser validations for truncated load-command regions and invalid cmdsize values (unaligned, out-of-bounds, smaller than the command structure).
• Add LCStr validation to reject malformed string offsets within load commands.
• Add yaml2obj YAML sources and prebuilt .macho fixtures, plus new tests covering the above cases.

Reviewed changes

Copilot reviewed 4 out of 25 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/test_macho.rb	Adds regression tests for invalid load command sizes/bounds, malformed lc_str offsets, and a few minimal/endianness/build-version/rpath fixture checks.
lib/macho/macho_file.rb	Hardens load command parsing by validating declared command region length, per-command truncation, alignment, and size bounds before parsing.
lib/macho/load_commands.rb	Adds strict LCStr offset validation to raise a targeted error for malformed load-command strings.
lib/macho/exceptions.rb	Introduces LoadCommandSizeError for invalid cmdsize cases.
test/bin/yaml2obj/Makefile	Adds a simple build rule to generate .macho fixtures from the YAML sources via yaml2obj.
test/bin/yaml2obj/load-cmdsize-too-small.yaml	YAML source for a fixture with cmdsize smaller than the command structure.
test/bin/yaml2obj/load-cmdsize-too-large.yaml	YAML source for a fixture with cmdsize exceeding the declared load-command region.
test/bin/yaml2obj/truncated-load-commands.yaml	YAML source for a fixture where ncmds is declared but sizeofcmds is zero.
test/bin/yaml2obj/truncated-load-command-region.yaml	YAML source for a fixture where sizeofcmds exceeds available file data.
test/bin/yaml2obj/unaligned-cmdsize.yaml	YAML source for a fixture with an unaligned load command size.
test/bin/yaml2obj/invalid-lcstr-offset.yaml	YAML source for a fixture with an invalid lc_str offset (e.g., 0).
test/bin/yaml2obj/minimal.yaml	YAML source for a minimal valid Mach-O fixture.
test/bin/yaml2obj/big-endian.yaml	YAML source for a big-endian fixture to exercise byte order parsing.
test/bin/yaml2obj/build-version.yaml	YAML source for a fixture containing LC_BUILD_VERSION metadata.
test/bin/yaml2obj/rpath.yaml	YAML source for a fixture containing an LC_RPATH command.

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[woodruffw]

@copilot deconflict and rebase this PR.

[Copilot]

@copilot deconflict and rebase this PR.

Done in 6e3de18: I deconflicted the branch against main, resolved the test/test_macho.rb conflict, and pushed the updated branch.