Fix: don't split URI params inside quoted-string values

[nixfeo-root]

Problem

parse_params (src/sip/uri.rs) splits the param string on ; unconditionally, so an RFC 3261 quoted-string param value containing a semicolon is broken into two bogus params:

sip:alice@example.com;x-route="a;b"
  → Param::Other("x-route", Some("\"a"))   // wrong
  → Param::Other("b\"", None)              // wrong

The mis-parse is easy to miss because it is invisible in Display round-trips — the two broken halves re-join with ; separators and reconstruct the original text. It only shows up in param count/values, which is exactly what dialog/registrar logic reads.

Per RFC 3261 §25.1, generic-param = token [ EQUAL gen-value ] with gen-value = token / host / quoted-string, so semicolons inside quoted values are legal. Real-world traffic in this class includes Linphone's Contact ;+sip.instance="<urn:uuid:…>" (survives today only because it happens to contain no inner ;) and proprietary ITSP params.

Fix

A small quote-aware splitter used by parse_params:

• no new allocation beyond the existing Vec, no regex/nom dependency;
• unquoted input splits exactly as before (all existing sip::uri tests pass unchanged);
• a dangling unbalanced quote degrades to the previous behavior (split disabled only inside balanced quotes) instead of erroring.

Tests

4 new tests in sip::uri::tests:

• quoted value with an inner ; stays one param with the value intact;
• real-world Linphone +sip.instance shape;
• unquoted multi-param splitting unchanged;
• dangling-quote graceful degradation.

cargo test --lib sip::uri: 30 passed. (The dialog::tests::test_client_dialog failures I see locally are present on pristine main in my environment too — unrelated to this change.)

Context: we're adopting rsipstack as the SIP stack for a production Rust CPaaS (replacing a vendored rsip fork that carried a nom-based version of this same fix) — happy to adjust style/scope as you prefer.