Add property-based tests for linker/ELF invariants

[katsyoshi]

Goal:
Add property-based tests to improve confidence in linker and ELF invariants beyond fixed fixtures.

Scope:

• Introduce property-based generators for minimal ELF/linker inputs (sections, symbols, relocations).
• Validate core invariants after link/write/read roundtrip:
  • section-header consistency (offset/size/entsize/link/info)
  • relocation range/type constraints
  • dynamic tag consistency with linked sections (e.g. DT_RELA*, DT_JMPREL/DT_PLT*)
• Start with deterministic seed + bounded cases for CI stability.

Acceptance criteria:

• Property-based tests run in CI with stable runtime budget.
• Failures report minimized reproducible seed/case.
• Existing fixture-based tests remain and complement property tests.

Notes:

• Track this as a separate stream from feature implementation so regressions are caught early during refactors.