Avoid retaining surrounding contact info in parsed numbers

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Summary

• store only the phone number matched by NSDataDetector in PhoneNumber.numberString
• prevent surrounding contact text such as names or email addresses from being retained after parsing
• add a regression test covering contact text around a valid phone number

Why

When parsing input that contains a phone number embedded in contact text, parsing already uses the detector match for validation, but the returned PhoneNumber could keep the original input string. If callers log, encode, or turn numberString into a tel URL, surrounding contact data may be exposed unnecessarily.

Testing

Not run locally because this environment is Windows and does not have Swift/Xcode installed.