Improve buffered reader API

[Guest0x0]

• add @io.BufferedReader::find_opt, which returns None on EOF, so that EOF can be handled more robustly
• add @io.BufferedReader::read_line

[coveralls]

Pull Request Test Coverage Report for Build 583

Details

• 13 of 14 (92.86%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 78.866%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/io/buffered_reader.mbt	13	14	92.86%

Totals
Change from base Build 582:	0.2%
Covered Lines:	1168
Relevant Lines:	1481

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💛 - Coveralls