fix(relay): preserve query strings during URL normalization

[cuishuang]

Summary

Fix relay URL normalization so query parameters are not modified accidentally.

The previous implementations used string-wide trim_end_matches('/') and replace() calls. These operations could alter query values or nested URLs, for example:

wss://relay.example/?next=/

could become:

wss://relay.example?next=

and:

wss://relay.example/path?redirect=wss://other.example/

could have its nested query URL rewritten.

The updated code parses URLs with url::Url, changes only the URL scheme and intended path component, and preserves query strings.

Related issue

Fixes #

Testing

• cargo test -p buzz-core relay::tests --lib
• cargo test -p buzz-cli client::tests --lib
• cargo test -p buzz-acp relay::tests --lib
• cargo clippy -p buzz-core -p buzz-cli -p buzz-acp --all-targets -- -D warnings

Regression coverage includes:

wss://relay.example/?next=/
wss://relay.example/?next=/foo/
wss://relay.example/?url=wss://other.example/

[github-actions]

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