Handle non Unicode env keys/values

[Jongy]

(disregard the code / commit message - I'll clean up & add tests once we agree on the implementation 😄 )

I hit the same issue as described in the linked ticket - with key PWD having a non-UTF-8 value ("invalid" from now on).

Technically, keys can be invalid too in Linux. The naive implementation I provided here filters out all invalid keys & values. Keys in config-rs are Strings so it always makes sense to filter invalid ones, as they won't be used by this library AFAIU.
As for values - I'm unsure if plainly ignoring invalid values is okay. If the value is set in a key that would have been used by the current config consumer, then ignoring it (as if the user did not provide a value through env) is not okay.
Ideally - the logic would be:

1. Valid key & value - continue
2. Invalid key - drop
3. Invalid value - drop if key is not consumed, otherwise panic.

Let me know what you think :) I can try looking into point 3.

Resolves: #579

[coveralls]

Pull Request Test Coverage Report for Build 13209377001

Details

• 10 of 13 (76.92%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 65.124%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/env.rs	10	13	76.92%

Totals
Change from base Build 13059823868:	0.1%
Covered Lines:	943
Relevant Lines:	1448

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💛 - Coveralls

[epage]

I'm sorry, I overlooked that I was reviewing two different PRs (#641) for the same problem.

The tests in #641 were able to also cover Windows which could be nice.

[Jongy]

Thanks for the review @epage , I addressed all comments.

The tests in #641 were able to also cover Windows which could be nice.

Fixed the tests here to support Windows. I haven't set up Wine to run them so I'll wait to see how it goes in the CI.

[epage]

Thanks!

[Jongy]

Thanks again for the review, and thanks for releasing, I'll proceed to update atuin to use the new version.