Consider Adding L4S and NQB Support

Hi - Some networks are working to test/deploy the IETF L4S standard for low latency networking, which creates a 2nd network queue at bottleneck links for packets marked with ECT(1) or DSCP-45 to use a low latency queue with a shallow queue depth. This should in theory improve working latency dramatically.

Perhaps it is worth considering in the future adding support for L4S and NQB. Initially it may just be probing to see if the marks work E2E (a la Is My BGP Safe Yet from CF). Then later test the performance effects.

Timing - The Comcast network is planning to trial L4S from mid-June so one way to test it may come up soon (you can also test in a lab of course).

References:
RFC [9330](https://www.rfc-editor.org/info/rfc9330), [9331](https://www.rfc-editor.org/info/rfc9331), [9332](https://www.rfc-editor.org/info/rfc9332), [draft-ietf-tsvwg-nqb](https://datatracker.ietf.org/doc/draft-ietf-tsvwg-nqb/)