Backward Compatible - Http3SettingsFrame abstraction (#15835) - #353

* [x] Provide a cleaner, more maintainable implementation of
`Http3SettingsFrame`.
* [x] Replace the previous untyped `LongObjectHashMap`-based approach
with a typed `Http3Settings` abstraction.
* [x] Improve API clarity and future extensibility for HTTP/3 settings
handling (similar to Http2Settings)

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* [x] Introduced `Http3Settings` class to encapsulate and manage HTTP/3
settings.
* [x] Deprecated legacy untyped accessors (`get()`, `put()`) in favor of
typed methods such as `qpackMaxTableCapacity()` and
`enableConnectProtocol()`.
* [x] Updated `DefaultHttp3SettingsFrame` to use the new `Http3Settings`
internally.
* [x] Added detailed Javadoc to guide migration to the new typed API.
* [x] Added comprehensive test coverage for `Http3Settings` and its
integration with `Http3SettingsFrame`.

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* [x] **Backward-compatible** – existing code using `get()`/`put()`
still works (marked deprecated).
* [x] **Forward-compatible** – encourages use of typed accessors.
* [x] **No behavioral change** – internal structure and API clarity
improved only.

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Port of netty/netty#15835