feat: Cache `Intl.*` constructors

[amannn]

Fixes #215

Intl.* constructors like Intl.DateTimeFormat are now cached across components in order to improve rendering performance (see benchmark).

Details:

• The message format cache that was already available has now been integrated with the cache for Intl.* constructors.
• Cache lifetime:
  • Client: The cache is released when the locale prop of the provider changes. For long-running apps with a persistent provider at the root, this can reduce the memory footprint (e.g. in React Native).
  • Server: Lifetime of the request.
• The .format calls are currently not cached. The reason is that while Intl.* constructor caching can work across various component instances and formatting calls, .format calls typically only affect a single call site. The overhead of memoization (serialization of args, diffing, bundle size) therefore might not be a good tradeoff here. In this area, avoiding re-renders is much more relevant, with the ideal solution being React Compiler.

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