docs: sync README API map with current exports

[kelsos]

Summary

Pre-release hygiene: the API map table in `packages/plainfp/README.md` hadn't been updated since a few of the 0.1.0 additions landed. This PR aligns the Result and Option rows with what the barrels actually export.

Changes

• Result row gains: `tap`, `tapError`, `toOption`
• Option row gains: `tap`, `tapNone`, `all`, `any`, `zip`, `toResult`

All other namespaces (result-async, arrays, records, strings, predicates, functions, brand, non-empty-array, tagged, interop/zod) were already accurate — verified by cross-referencing each row against its `src//index.ts`.

Why now

Two-line fix before cutting 0.1.0 so the published npm page doesn't advertise an incomplete API surface. Integration tests PR to follow.

Test plan

• All required CI checks pass (trivial change)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.68%. Comparing base (003916b) to head (30549a3).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #11   +/-   ##
=======================================
  Coverage   91.68%   91.68%           
=======================================
  Files          23       23           
  Lines         397      397           
  Branches       90       90           
=======================================
  Hits          364      364           
  Misses         11       11           
  Partials       22       22           

Flag	Coverage Δ
unittests	91.68% <ø> (ø)

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[codspeed-hq]

Merging this PR will not alter performance

✅ 48 untouched benchmarks

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_{Comparing docs/api-map-sync (30549a3) with main (5153437)¹}

Footnotes

1. No successful run was found on main (30549a3) during the generation of this report, so 5153437 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩