fix(libc): resolve guest paths case-insensitively on Linux

[dannyhashim08]

What

On Linux, resolve guest paths case-insensitively when the exact host path is missing. Exact existing paths stay on the fast path. If a directory contains multiple names that differ only by case, preserve the requested path so resolution still fails instead of choosing arbitrarily.

Closes #1047

Tested

Not tested.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed in TechnicalDebt
• No notes, investigation .md files or images added to the repository
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: none
• AI-assisted: yes

[oneandonlydean]

Closing: #1079 already does this for #1047, with a test, and #1321 is a second version of it. If yours handles a case those miss, please say so on #1079.