fix(mlog): align qlog event output with draft-pardue-moq-qlog-moq-events-03

[englishm-cloudflare]

Summary

Align mlog event output with draft-pardue-moq-qlog-moq-events-03 (the qlog events spec matching our MoQT draft-14 implementation) and switch to epoch-relative timestamps.

Addresses feedback from @LPardue who reviewed sample mlog output during IETF 125.

Changes

Event structure alignment (commit 1)

• File header: update to qlog-main-schema-13 format (file_schema URN, serialization_format, versioned event_schemas with moqt-03)
• Remove redundant event_type from event data — the name field already carries the event type
• Nest control messages under a message object with a type discriminator, matching the spec's $MOQTControlMessage structure
• Use request_id in qlog output (mapped from internal subscribe_id at the serialization boundary)
• Remove header_type from subgroup_header events (not present in any version of the spec)
• Add extension_headers_length to subgroup object events (required field in -03)
• Format data types per spec: track_namespace as [MOQTByteString], track_name as MOQTByteString, locations as MOQTLocation (Sections 5.4/5.5), number_of_parameters on all control messages that require it

Typed parameters and epoch timestamps (commit 2)

• Typed parameters: format setup params as MOQTSetupParameter objects and message params as MOQTParameter objects per spec Sections 5.2/5.3. Known types (path, max_request_id, delivery_timeout, max_cache_duration) get named objects; unknown parameters use the spec's fallback format. Extension headers formatted as MOQTExtensionHeader per Section 5.7.
• Epoch-relative timestamps: switch from Instant-based relative timestamps (ms since connection start) to absolute epoch-ms via cached SystemTime offset + Instant::elapsed(). The header declares time_format: "relative_to_epoch" with Unix epoch per qlog-main-schema-13 Section 7.1, so consumers can use the time field directly as a native timestamp.
• Serialization cleanup: remove Deserialize from Event/EventData (serialization-only; untagged enum is ambiguous for structurally identical variant pairs), redact authorization token values in qlog output (log only token_length), compute extension_headers_length analytically via varint_wire_len().
• Update MLOG_SETUP.md examples to match the new format throughout.

Example output

Header:

{"file_schema":"urn:ietf:params:qlog:file:sequential","serialization_format":"JSON-SEQ","title":"moq-relay","description":"MoQ Transport events","trace":{"vantage_point":{"type":"server"},"common_fields":{"time_format":"relative_to_epoch","reference_time":{"clock_type":"system","epoch":"1970-01-01T00:00:00.000Z"}},"event_schemas":["urn:ietf:params:qlog:events:moqt-03"]}}

CLIENT_SETUP parsed:

{"time":1775794492056.19,"name":"moqt:control_message_parsed","data":{"stream_id":0,"message":{"type":"client_setup","number_of_supported_versions":1,"supported_versions":["DRAFT_14"],"number_of_parameters":1,"setup_parameters":[{"name":"max_request_id","value":100}]}}}

PUBLISH_NAMESPACE parsed:

{"time":1775794492057.16,"name":"moqt:control_message_parsed","data":{"stream_id":0,"message":{"type":"publish_namespace","request_id":0,"track_namespace":[{"value":"moq-test"},{"value":"interop"}],"number_of_parameters":0,"parameters":[]}}}

Version targeting

This targets moq-qlog-moq-events-03 (Oct 2025), which references moq-transport-14 and qlog-main-schema-13. Later draft versions (-05, -06) introduce fields like subgroup_id_mode and object_id_delta that don't exist in -03; those are intentionally not included here.