fix(moq-transport): preserve subgroup object IDs

[englishm-cloudflare]

Summary

• preserve decoded non-zero and sparse subgroup Object IDs in the serve model
• encode checked Object ID deltas relative to the previous transmitted Object after filtering
• propagate fatal subgroup Object ID overflow and cover ingress plus filtered retransmission over in-process transport sessions

Validation

• cargo fmt --all --check
• focused contiguous, sparse, filtered, non-monotonic, and overflow vectors
• cargo test -p moq-transport
• cargo test --workspace
• workspace Clippy with the four pre-existing baseline lints explicitly allowed

Scope

This intentionally does not change subgroup header modifiers, FIRST_OBJECT, priority, properties, completion semantics, datagrams, mixed delivery, FETCH, logging, or moq-test-client behavior.

Base: cloudflare/moq-rs@9ed84735722adf0aa756c5781eaf31c8e12a00f4