Add recursive directory deletion

[rovolsw]

Related PRs:

• 88: Add nob_delete_dir #103 (revelant to)
• Add incremental directory iterator #145 (depends on)

Related commit:

• [Suggestion] A function to recursively delete a directory? #88 (solved it)

This PR features a recursive directory deletion to nob.h based on the incremental directory iterator in #145, which is built upon DFS.

New functions:

• [API] nob_delete_directory(): deletes empty directories
• [API] nob_delete_directory_recursively(): deletes directories recursively
• [INNER] nob__delete_directory_recursively(): implementation of nob_delete_directory_recursively()

Example:

nob_delete_directory_recursively("./build");
nob_delete_directory_recursively("./bin");
nob_delete_directory_recursively("./obj");
// etc.

[Qfresquin]

This is very useful. I recently ran into the exact need for nob_delete_directory_recursively() while building a test runner on top of nob.

My project generates temporary build artifacts per test suite (probes, try_compile executables, coverage data, etc.) and I needed a clean sandbox mechanism. Without recursive deletion, this required custom platform-specific cleanup logic outside of nob.

The incremental iterator from #145 + DFS-based recursive deletion here is exactly the right architectural direction compared to the earlier nob_read_entire_dir() approach.

Looking forward to this being merged after #145.