Fix FileSystemService dirent parsing on macOS

[sentry]

This PR addresses an EXC_BAD_ACCESS (KERN_INVALID_ADDRESS) crash occurring in FileSystemService.listDirectoryWithIgnoreDetection and scandirListDirectory on macOS.

Root Cause:
On macOS, the dirent struct returned by readdir is variable-length, with its actual size determined by the filename length. The previous implementation copied direntPtr.pointee, which attempts to read a fixed-size dirent struct. This could extend beyond the kernel's allocated buffer for the specific directory entry into unmapped memory, leading to a crash.

Solution:

1. Refactored Helper Signatures: decodeDirentName, descriptorRelativeMode, and fileTypeFallback now accept UnsafeMutablePointer<dirent> or Data (for name bytes) instead of dirent by value.
2. Safe dirent Field Access: On macOS, decodeDirentName now uses raw pointer arithmetic to read d_namlen and d_name bytes directly from the dirent pointer, ensuring reads are strictly within the allocated bounds. This avoids copying the entire variable-length struct.
3. Updated Call Sites: The main loops in listDirectoryWithIgnoreDetection and scandirListDirectory no longer perform direntPtr.pointee copies. Instead, they pass the dirent pointer directly to the updated helper functions and read d_type via raw pointer access on macOS.

Fixes REPOPROMPT-9V