Housekeeping: small correctness and hygiene items

[developerjamiu]

Small items found during the audit, grouped because none justifies its own issue.

• lib/src/models/item_span.dart:48 uses bool operator ==(covariant ItemSpan other). The covariant inserts a runtime downcast, so comparing an ItemSpan with any other type throws TypeError instead of returning false. Use Object other with an is check.
• lib/src/models/item_span.dart:57 omits rawValue from hashCode while == includes it. Legal, but spans differing only in rawValue collide unnecessarily.
• pubspec.yaml depends on url_launcher_ios directly. It is an endorsed implementation of url_launcher; depending on it pins an implementation package callers should never see.
• example/lib/smart_text.dart is 104 lines and imported by nothing.
• lib/src/extensions/string.dart:4 matches startsWith('http'), which also matches httpfoo, and the Uri.parse on the next line can throw inside build.
• lib/src/extensions/item_span_default_config.dart:85 uses canLaunchUrl then launchUrl, the check-then-act pattern url_launcher's own docs advise against.
• lib/src/extensions/item_span_default_config.dart:45-47 has a comment in the datetime branch that talks about "the formatted phone number" and "the phone field".
• TextClassifier.swift and NSDataDetectorExtension.swift both open with // SmartTextFlutterBridge.swift and // Runner headers from whatever file they began as.
• flutter_lints: ^2.0.0 is several majors behind.

Good first issue material.

Found during the v0.4.0 codebase audit.