walker-skip should accept nested directories, not just a single path component

[jyn514]

Checklist

• I have read through the manual page (man fzf)
• I have searched through the existing issues
• For bug reports, I have checked if the bug is reproducible in the latest version of fzf

Output of fzf --version

0.56.3 (add1aec)

OS

• Linux
• macOS
• Windows
• Etc.

Shell

• bash
• zsh
• fish

Problem / Steps to reproduce

$ mkdir -p a/b
$ touch a/b/foo
$ fzf --walker-skip a/b

i expect that this does not return a/b/foo. instead it does show it.

if i use --walker-skip b, it correctly ignores the file. but i don't want to ignore all directories named b, only this particular directory.