Urllib3-future

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- Fixed the ability to override properly the ``:authority`` special header via the legacy ``Host`` header.

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- Removed workaround for a bug that existed in qh3 < 1.0 with cryptography in a concurrent (thread) environment.
- Avoid loading qh3 at runtime in order to improve import delay. It was used to probe HTTP/3 support. We compute it lazily from now on.
- Added the possibility to use the ``preemptive_quic_cache`` MutableMapping to exclude endpoints.
If your implementation discard the recently set key/entry it will prevent the connection from upgrading itself.

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- Improve (large) data download performance by increasing the default blocksize.
- Improve HTTP/1.1 performance by reducing the amount of time we want to infer "if next cycle" should be triggered.

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- Improve ``traffic_state_of`` function to improve the overall performance in a highly concurrent context.

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- Passing a ssl context containing manually loaded root certificates no longer is ignored with HTTP/3 over QUIC.

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- Overall performance improvement with HTTP/2 in a highly concurrent context.