perf(isEmail, isFQDN, normalizeEmail): up to 2x faster by skipping the default-options copy

[deadstrobe5]

When called without options, isEmail, isFQDN and normalizeEmail ran merge(undefined, defaults), which allocates a new object and copies every default into it on each call. None of these functions mutate options or pass it on to code that does (isEmail builds a fresh object for its isFQDN call), so they can read the module-level defaults directly. Calls that pass options still go through merge unchanged, and any falsy options value previously produced exactly a copy of the defaults, so results are the same.

Benchmark (Node 26, Apple M5, A/B interleaved in one process, 20 rounds × 100 ms, median ratio; an A/A control gave 1.00 with ±2–4% noise):

Function	Before	After	Speedup
isEmail	433 ns	339 ns	1.27x
isFQDN	208 ns	138 ns	1.50x
normalizeEmail	313 ns	150 ns	2.06x

isURL is unchanged on purpose: it passes its own options object to isFQDN, so it keeps the current path.

A differential test of ~186,000 inputs and option combinations (calls with and without options interleaved in one process) against the previous build found no differing results. npm test passes (323 tests, 100% coverage on the changed files) and eslint is clean.

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9ff3424) to head (d404b3f).

Additional details and impacted files

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##            master     #2932   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          114       114           
  Lines         2599      2599           
  Branches       658       660    +2     
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  Hits          2599      2599           

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