[Bug]: Application Error Code (0x1d) Allowed in QUIC Initial Packets, Violates RFC 9000

[jiangshaoqi]

What happened?

The library incorrectly allows sending CONNECTION_CLOSE frames with Application Error codes (0x1d) in QUIC Initial packets, which violates RFC 9000 protocol rules.

Expected Behavior:

According to RFC 9000 Section 10.2.3, only Transport Error codes (0x1c) should be allowed in Initial/Handshake packets.

Actual Behavior:

The library permits Application Error codes (0x1d) in Initial packets, causing potential interoperability failures with compliant QUIC implementations (e.g., clients/servers may reject the connection or trigger protocol errors).

Steps To Reproduce

When calling connection close function, with err_code 0x1d:
xqc_write_conn_close_to_packet(xqc_connection_t *conn, uint64_t err_code)

Relevant log output