Align email scanner contract

[alyldas]

Summary

• Keep the email scanner contract names as backward-compatible shared-shape adapters.
• Export EmailScanHints and keep scanner range and sink shapes aligned with the shared range contract style.
• Replace the local email masking wrapper with the shared core censorCodePointRanges() helper.
• Add regression coverage for scanner contract typing and public censor wrapper alignment with scanner ranges.

Validation

• npm ci
• npm run check with a temporary npm cache because the local user cache has permission-owned files
• npm run benchmark:email
• npm pack --dry-run with a temporary npm cache

Benchmark Evidence

Baseline origin/main:

• check short clean: 0.0002 avg ms
• check hinted short clean: 0.0002 avg ms
• check long clean: 0.0059 avg ms
• check direct email: 0.0032 avg ms
• check late-match email: 0.1332 avg ms
• censor short clean: 0.0003 avg ms
• censor long clean: 0.0206 avg ms
• censor direct email: 0.0066 avg ms
• censor late-match email: 0.2139 avg ms

This branch:

• check short clean: 0.0004 avg ms
• check hinted short clean: 0.0002 avg ms
• check long clean: 0.0057 avg ms
• check direct email: 0.0036 avg ms
• check late-match email: 0.1314 avg ms
• censor short clean: 0.0003 avg ms
• censor long clean: 0.0206 avg ms
• censor direct email: 0.0069 avg ms
• censor late-match email: 0.2660 avg ms

The runtime change delegates masking to the existing core helper; scanner matching behavior is unchanged.

Compatibility Notes

• Existing public API remains backward compatible.
• createEmailFilter(), emailFilter(), filter, createEmailScanner(), scanEmailRanges(), collectEmailRanges(), and scanEmailRangeMatches() remain available.
• Existing EmailScanInput, EmailRangeScanResult, EmailRangeMatch, and EmailRangeMatchSink names remain available.

Closes #35

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feat: align email scanner contract
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