chore(internal): fix mod export skips across checkouts

[tomas-zijdemans]

lint:mod-exports matched its skip list against absolute paths, so the directory you cloned std into could switch the check off. With a checkout at /private/tmp/_probe/std, the /(\/|\\)_/ pattern matches /_probe and every file gets skipped. An unexported async/planted.ts passes without a warning. A parent directory with "unstable" in its name does the same thing through /unstable/. CI runs on GitHub-hosted runners (/home/runner/work/std/std), so this only hits local runs and self-hosted runners, which check out under _work.

The patterns now run against the path relative to the repo root (uuid/v1.ts), with / separators on every platform. That also drops the (\/|\\) alternation from each entry.

Also in here:

• /mod\.ts$/ becomes /\/mod\.ts$/. The old pattern also skipped any file whose name ends in mod.ts, so a stable fs/chmod.ts would never be checked.
• Removes the uuid/v6.ts entry. That file doesn't exist. The v6 module is unstable_v6.ts, which /unstable/ already covers.
• new Set<string>() instead of new Set().

Testing: deno task lint:mod-exports passes on main. I planted an unexported async/planted.ts and fs/chmod.ts in worktrees at /private/tmp/_probe/std and /private/tmp/unstable-probe/std, and both files warn in both. I also removed each named skip entry one at a time to confirm it still suppresses a real warning.

Heads-up: my #7335 (dotenv removal) edits the dotenv/load.ts line in this list, so whichever lands second needs a one-line rebase.

I used Claude Code to help investigate and write this change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.04%. Comparing base (f834d02) to head (3fbdeba).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7340      +/-   ##
==========================================
- Coverage   95.04%   95.04%   -0.01%     
==========================================
  Files         619      619              
  Lines       52012    52012              
  Branches     9450     9450              
==========================================
- Hits        49434    49433       -1     
  Misses       2031     2031              
- Partials      547      548       +1     

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