fix: refactor MachO to remove leak

[lilfer]

Fixes #115

Resolves a memory leak caused by using Box::leak in Mach-O manipulation routines.

Problem

• MachO can't both own both MachFile and the binary buffer it borrows without self-referencing, so the previous implementation leaked the buffer to satisfy the 'static lifetime.
• Methods in MachOExt called self.data = Box::leak(...) each time binary load commands were modified.

This caused memory accumulation over time when performing repeated signing operations.

Changes

• Changed MachO to store data: Vec<u8> instead of MachFile<'static>, dynamically parsing MachFile<'_> on demand in macho_file(&self).
• Updated MachOExt methods to return the modified data instead of mutating and leaking it.
• Added a modify_binaries helper in MachO to apply closures and update self.data. Since every edit already wrote to disk, I removed write_changes and merged it into this helper, but with this setup it should be easy to instead chain edits before saving.