fix(msan): harden loader path handling to avoid uninitialized reads

[MrSpideyNihal]

This PR fixes repeated MemorySanitizer uninitialized-read reports in the loader execution-path flow by hardening path construction and storage across configuration, loader core, and ext loader.

What changed

1.ext_loader: bounded path conversion using LOADER_PATH_SIZE

• Replaced direct path conversion with bounded string construction before filesystem path conversion.
• Added cstring include required for strnlen.

2.loader core: normalize deferred execution paths before storage

• Zero-initialize temporary loader_path buffers.
• Avoid raw push of external path pointers into fixed-size vector slots.
• Copy paths into normalized, null-terminated loader_path buffers before vector insertion.

3.configuration: bound and terminate child path copy

• Use bounded length for copied path data.
• Explicitly write null terminator after memcpy.

Why
MSan showed repeated use-of-uninitialized-value in ext_loader execution path handling. Root cause is partially initialized path-buffer propagation through loader path flow. This PR prevents reading beyond initialized bytes and aligns bounds with loader path size contracts.