feat: Implement AsLockedWrite generically too

[DaniPopes]

Missed in #224. Implement the same changes for AsLockedWrite.

I've added tests to make sure that these types both implement RawStream and that AutoStream implements std::io::Write.

[coveralls]

Pull Request Test Coverage Report for Build 11506467501

Details

• 0 of 8 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 51.803%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/anstream/src/stream.rs	0	8	0.0%

Totals
Change from base Build 11502774998:	-0.2%
Covered Lines:	1221
Relevant Lines:	2357

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💛 - Coveralls