Invalidate URI caches after component changes

[OskarEichler]

Summary

Invalidate dependent normalization and composite caches when URI components change. Host changes could retain an old normalized authority; scheme changes could retain an old default-port decision. Reset site caches during destructive replacement too, preserving sentinel-based instance variables from #486.

Reproduction

require 'addressable'
uri = Addressable::URI.parse('https://one.example')
uri.normalize
uri.host = 'two.example'
p uri.normalize.to_s
# Before: https://one.example/; after: https://two.example/

Verification

• Ruby 4.0.6 through rbenv; existing suite: 1,433 examples / 0 failures / 5 existing pending with pure Ruby IDNA, 1,466 examples / 0 failures / 5 existing pending with idn-ruby 0.1.5 + libidn.
• 285 focused external assertions pass on this individual patch; the combined installed-release branch also passes all focused cases and both existing suites.
• Comparative RuboCop Lint: 15 existing offenses before and after; no new offense (line references move). Syntax and git diff --check pass.

Compatibility and limitations

No intended breaking change. Corrects stale results after setters/merge!/join!/normalize!. Caches remain lazy; component strings and normalization rules are unchanged. This does not make externally mutated component strings safe or make URI instances thread-safe.

No dependency/version/data updates. No repository tests were added or changed: the commissioning repository explicitly prohibits new/modified tests, so reproduction checks run outside this repository. Other Ruby versions/platforms were not run locally; upstream CI may require maintainer approval. The existing normalization proposal #589 and IDNA2008 proposal #496 are separate and unchanged.