Fix mutating path of URL without authority (idempotency, empty path segments)

[theskim]

From Issue #984

[codecov]

Codecov Report

Attention: Patch coverage is 93.47826% with 3 lines in your changes missing coverage. Please review.

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Files with missing lines	Patch %	Lines
url/src/path_segments.rs	88.88%	2 Missing ⚠️
url/src/lib.rs	96.42%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #996   +/-   ##
=======================================
  Coverage        ?   80.85%           
=======================================
  Files           ?       24           
  Lines           ?     4272           
  Branches        ?        0           
=======================================
  Hits            ?     3454           
  Misses          ?      818           
  Partials        ?        0           

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[valenting]

If I'm not mistaken, these failing tests should also be made to pass as part of this test

rust-url/url/tests/expected_failures.txt

Lines 39 to 40 in da64903

	<non-spec:/.//p> set hostname to <h>
	<non-spec:/.//p> set hostname to <>

That's about mutating the host, not the path, but I think the behaviour is closely related to this one.

[valenting]

Sorry for the delayed review. See inline:

[theskim]

@valenting, should I be worried about this failure?

[valenting]

It seems the MSRV for libc changed
rust-lang/libc@77b3ea4#diff-06572a96a58dc510037d5efa622f9bec8519bc1beab13c9f251e97e657a9d4edR9

Feel free to also increase ours to 1.63

[valenting]

Note: I think we need to add #943 to this PR considering we backed it out in #999

[theskim]

Need to add tests to check scheme_end, username_end, host_start, etc.