fix(egfx): respect client frame acknowledgement limits

[Piclaw (piclaw-bot)]

A client advertising a one-frame ACK window can currently be sent frames using the server's larger configured window. An AVC producer also receives the same None for a full window as for a permanent submission error, which makes ordinary backpressure difficult to handle without replacing the encoder.

This PR is based directly on master and is independent of #1413. It contains no credential, binder or acceptor changes.

• Apply the nonzero core Frame Acknowledge capability as a ceiling on the operator-configured EGFX window, including legacy graphics factories. Configured zero remains unlimited only when the client has no ceiling; resize preserves the negotiated ceiling.
• Reject unknown/stale ACKs before they can suspend or mutate tracking. Preserve valid suspension/resumption for frames issued in the current channel generation, and clear channel-owned state on close.
• Report client queue depth as Unavailable: our client counts frames, while the protocol field measures bytes. This is distinct from Suspend.
• Add typed AVC420, AVC444 and AVC444v2 submission errors, including Backpressured, while retaining the existing Option methods as compatibility wrappers. Mixed-codec send APIs are unchanged.

WRDP exposed the configured-three/client-one case during desktop dragging. These changes let the producer retain its encoder and retry/recover after an ACK instead of treating backpressure as encoder failure.

Focused checks passed locally (Rust 1.96; the repository pins 1.94.1):

cargo test -p ironrdp-egfx --lib                               # 55 passed
cargo test -p ironrdp-testsuite-core --test integration_tests_core -- egfx::server  # 92 passed
cargo test -p ironrdp-server --lib --features egfx -- frame_ack # 2 passed
cargo test -p ironrdp-server --lib --features egfx -- gfx::tests # 2 passed
cargo fmt --all
git diff --check

Regressions cover window/zero semantics, activation clamps, resize, legacy factories, stale suspend/resume ACKs across close/reopen, restored tracking after valid resume, and typed rejection without queued output. A read-only review caught the legacy-factory and suspended-ACK resume paths; both are corrected and covered here.

Happy to adjust the additive error API to the project's preferred shape during review. This PR can be reviewed and merged separately from the session-binding work.