moq-lite-03 (#15)

* Draft-03: Add delivery properties

* AI review.

* Draft-03: ALPN handshake, FETCH, PROBE, group ranges, GROUP_DROP

Replace SETUP handshake with ALPN-based version negotiation (moq-lite-xx).
Add FETCH stream for single group download, PROBE stream for bitrate
measurement, start/end group ranges to subscriptions, and GROUP_DROP
for indicating unavailable groups. Unknown stream types are now non-fatal
to enable extension negotiation via stream probing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Remove instants; base expiration on arrival timestamps

Remove Instant Delta from FRAME and the Instant section from Delivery.
Expiration is now based on when the first byte of a group arrives
rather than per-frame instant values.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Clarify expiration: group age relative to latest group

Expiration is computed by comparing a group's arrival time to the
latest group's arrival time. A group is never expired until a newer
group (by sequence number) exists.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Use sequence + count for SUBSCRIBE_OK and GROUP_DROP

Replace start/end group with Group Sequence + Group Count for fewer
bytes on the wire. Count of 0 means unbounded.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Remove ANNOUNCE_INIT, add Hops to ANNOUNCE

Remove ANNOUNCE_INIT to simplify the protocol and avoid large messages.
The publisher now sends individual ANNOUNCE messages for all matching
broadcasts. Add Hops field to ANNOUNCE as a tiebreaker for multiple paths.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Rename GROUP_DROP to SUBSCRIBE_DROP, add type discriminator

Add a type field before message length to distinguish SUBSCRIBE_OK
(0x0) and SUBSCRIBE_DROP (0x1) on the subscribe response stream.
SUBSCRIBE_OK must be the first message; SUBSCRIBE_DROP before it
is invalid.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* More tweaks.

* Go back to end group to be consistent.

* Use start/end group for SUBSCRIBE_DROP.

* PR review

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: kixelated