fix: raise ParserError for empty string in parse()

[SAY-5]

Pull Request Check List

• Added tests for changed code.
• Updated documentation for changed code.

pendulum.parse("") raised ValueError: year 0 is out of range instead of ParserError; the common-format parser now rejects a match that captured neither a date nor a time component. Closes #849.

[codspeed-hq]

Merging this PR will not alter performance

✅ 1 untouched benchmark

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_{Comparing SAY-5:fix-parse-empty-string (4d6aa6a) with master (0a88aec)}