fix: shutdown and stream lifecycle handling

[richard-ramos]

Improves QUIC context shutdown safety and stream lifecycle behavior.

• Added explicit QUIC context running state.
• Split context shutdown from native resource destruction.
• Ignored late datagrams after context shutdown starts.
• Guarded engine operations when the context is no longer running.
• Fixed pending stream cleanup on server connection close.
• Improved stream EOF, blocked read, write, and flush error handling.
• Released GC refs when client dial creation fails.
• Fixed certificate DER conversion for nil/invalid X509 values.
• Added lifecycle and TLS coverage for the new shutdown and stream edge cases.

[Copilot]

Pull request overview

This PR hardens QUIC shutdown semantics and stream lifecycle behavior by introducing an explicit “running” state for contexts, splitting quiesce vs native teardown, and tightening error/edge-case handling (streams, connections, TLS cert conversion), with added tests covering the new behavior.

Changes:

• Introduces QuicContext.running with stop() (quiesce) and destroy() (native teardown), and guards engine operations/packet ingestion when not running.
• Improves stream/connection lifecycle correctness: pending stream cancellation on server close, stronger stream write/flush/wantwrite/wantread error handling, and safer client dial GC ref cleanup.
• Fixes/extends TLS certificate DER conversion behavior (nil/invalid handling) and adds lifecycle/TLS tests for shutdown + late datagram cases.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lsquic/context/context.nim	Adds running state, guards engine operations, and splits stop() from destroy().
lsquic/context/io.nim	Ignores datagrams when context is not running.
lsquic/client.nim	Updates client shutdown flow to stop() contexts before UDP close and destroy() after.
lsquic/server.nim	Updates listener shutdown ordering and fixes log message typo.
lsquic/context/client.nim	Ensures running=true and releases GC refs when dial fails.
lsquic/context/server.nim	Ensures running=true and cancels pending streams on server connection close.
lsquic/connection.nim	Processes engine after stream creation request to advance pending stream lifecycle.
lsquic/stream.nim	Tightens close/write error handling (flush/wantwrite) and fixes close typo.
lsquic/context/stream.nim	Improves blocked-read handling via wantread management and fixes log message.
lsquic/certificates.nim	Rejects nil X509 and ensures DER conversion only succeeds on positive length.
tests/test_lifecycle.nim	Adds coverage for late datagrams after context stop/destroy.
tests/test_tlsconfig.nim	Adds coverage for DER conversion success and nil rejection.
lsquic/helpers/transportaddr.nim	Fixes assertion message typo.
.github/workflows/lint.yml	Bumps NPH action version used in lint workflow.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.