fix: prevent dots from being URL-encoded in userinfo

[Copilot]

Dots (.) in usernames and passwords were incorrectly URL-encoded as %2E during serialization. Fixes gitbutlerapp/gitbutler#11419.

// Before: http://user%2Ename:pass%2Eword@example.com/repo
// After:  http://user.name:pass.word@example.com/repo
let url = gix_url::Url::from_parts(
    Scheme::Http,
    Some("user.name".into()),
    Some("pass.word".into()),
    Some("example.com".into()),
    None,
    "/repo".into(),
    false,
)?;

Changes

• gix-url/src/lib.rs: Replace NON_ALPHANUMERIC encoding with RFC 3986-compliant USERINFO_ENCODE_SET that preserves unreserved chars (. - _ ~)
• gix-url/tests/url/parse/http.rs: Add roundtrip tests for dots in username, password, and both
• gix-url/tests/url/parse/ssh.rs: Add roundtrip test for dots in SSH usernames
• gix-url/tests/fixtures/make_baseline.sh: Add baseline URLs with dotted usernames (ssh://user.name@host/repo, git://user.name@host/repo, user.name@host:repo)

Original prompt

Add tests to the gix-url baseline tests and serialisation tests that validate that . in user names won't be URL encoded. The same is true for passwords. See gitbutlerapp/gitbutler#11419 for reference.

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