fix(picker): cache apropos result to speed up :Telescope man_pages

[delphinus]

Description

:Telescope man_pages uses output from the command: apropos. This is too slow command to use for this.

~ ❯❯❯ hyperfine -w 5 -N 'apropos .'
Benchmark 1: apropos .
  Time (mean ± σ):      1.457 s ±  0.082 s    [User: 0.386 s, System: 1.004 s]
  Range (min … max):    1.317 s …  1.556 s    10 runs

This patch caches the output and reuse it until it becomes stale. Now it detects it is “stale” if the cache file mtime is older than 86400s before.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

I confirmed it works on macOS and Linux. But I didn't write unit tests.

• :Telescope man_pages opens fast because of cache
• Deleted cache, and :Telescope man_pages opens slowly again

Configuration:

• Neovim version (nvim --version): NVIM v0.11.0-dev-4649+g6719276040-Homebrew
• Operating system and version: macOS Sequoia 15.1.1

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)