Fix Mach-O section metadata and function discovery

[blankwall]

Summary

• represent Mach-O zero-fill sections with filesize == 0 while preserving their virtual size
• publish decoded LC_FUNCTION_STARTS entries through CLE's standard function_hints interface
• cover file-offset containment, ordinary section sizing, hint ordering, zero-sized hint metadata, and rebasing

Rationale

Mach-O section size is a virtual size. S_ZEROFILL, S_GB_ZEROFILL, and
S_THREAD_LOCAL_ZEROFILL occupy memory but have no file-backed bytes. Passing
their virtual size as CLE's file size makes them claim unrelated file offsets,
often including offset zero.

CLE already decodes LC_FUNCTION_STARTS, but previously retained those
addresses only in the Mach-O-specific lc_function_starts list. Publishing
them as source-labeled FunctionHint entries lets existing CFG consumers use
the linker-provided starts without Mach-O-specific integration.

Validation

• pytest -q tests/test_macho.py -k 'not relocatable_object' (14 passed, 1 deselected)
• verified all 11,199 decoded starts from a stripped AArch64 Mach-O are exposed as ordered function hints
• verified hints rebase by image_base_delta

The deselected test was added to CLE master by #787, but its
relocatable_object.macho fixtures are not yet present in the current
angr/binaries master.

[ltfish]

Thanks!