Remove unreliable assertions around Query and Fragment offsets

[MihaZupan]

Fixes #119547

#119547 (comment)

We have asserts that Query and Fragment offsets aren't populated if Flags.AllUriInfoSet isn't set (as we haven't finished parsing yet).

runtime/src/libraries/System.Private.Uri/src/System/Uri.cs

Lines 180 to 181 in 80dbb9f

Debug.Assert(offset.Query == 0);
Debug.Assert(offset.Fragment == 0);
The asserts have a race condition since a different thread may have done the parsing between us checking the flag and reading the offsets. Introduced in #117287.

Might have to backport that to 10.0 as well if it creates too much CI noise.

[Copilot]

Pull Request Overview

This PR fixes a race condition in URI parsing assertions by removing unreliable debug assertions for Query and Fragment offsets. The issue occurs when multiple threads access the same URI instance during parsing, causing assertions to fail when one thread checks parsing flags while another thread has already populated the offsets.

• Removes two debug assertions that check Query and Fragment offsets are zero
• Adds explanatory comment about the race condition with multi-threaded access
• Maintains other assertions that remain valid in multi-threaded scenarios

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[wfurt]

LGTM