try_assign_capacity triggers debug assertion

Hi!

One of our tests occasionally triggers this debug assertion. Unfortunately, I cannot share a minimal reproduction at the moment.

    thread 'tokio-runtime-worker' panicked at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/h2-0.4.13/src/proto/streams/prioritize.rs:448:9:
    state=Closed(ScheduledLibraryReset(CANCEL))
    stack backtrace:
       0: __rustc::rust_begin_unwind
                 at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/panicking.rs:697:5
       1: core::panicking::panic_fmt
                 at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/panicking.rs:75:14
       2: h2::proto::streams::prioritize::Prioritize::try_assign_capacity
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/h2-0.4.13/src/proto/streams/prioritize.rs:448:9
       3: h2::proto::streams::prioritize::Prioritize::poll_complete
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/h2-0.4.13/src/proto/streams/prioritize.rs:538:22
       4: h2::proto::streams::send::Send::poll_complete
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/h2-0.4.13/src/proto/streams/send.rs:339:14
       5: h2::proto::streams::streams::Inner::poll_complete
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/h2-0.4.13/src/proto/streams/streams.rs:905:34
       6: h2::proto::streams::streams::Streams<B,P>::poll_complete
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/h2-0.4.13/src/proto/streams/streams.rs:186:12
       7: h2::proto::connection::Connection<T,P,B>::poll
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/h2-0.4.13/src/proto/connection.rs:287:55
       8: <h2::client::Connection<T,B> as core::future::future::Future>::poll
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/h2-0.4.13/src/client.rs:1441:33
       9: <hyper::common::either::Either<F1,F2> as core::future::future::Future>::poll
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/hyper-1.8.1/src/common/either.rs:43:46
      10: <hyper::proto::h2::client::ConnMapErr<T,B> as core::future::future::Future>::poll
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/hyper-1.8.1/src/proto/h2/client.rs:275:32
      11: <core::pin::Pin<P> as core::future::future::Future>::poll
                 at /home/phueber/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/future/future.rs:124:9
      12: <hyper::proto::h2::client::ConnTask<T,B> as core::future::future::Future>::poll
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/hyper-1.8.1/src/proto/h2/client.rs:340:67
      13: <hyper::proto::h2::client::H2ClientFuture<B,T,E> as core::future::future::Future>::poll
                 at /home/phueber/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/hyper-1.8.1/src/proto/h2/client.rs:398:58

Start with h2-0.4.13/src/proto/streams/prioritize.rs at try_assign_capacity and follow its call from poll_complete, then inspect the related send and connection frames shown in the trace. The issue provides no reproduction, requested behavior, or test target, so the failure scenario and completion criteria must be established before implementation.