fix(om): preserve enriched Event Hubs token compatibility on Orleans 10.4

[egil]

Release Baseline

All OM packages in this release will consistently require Orleans 10.4.0; the Journaling dependency is 10.4.0-alpha.1. Consumers must upgrade Orleans along with OM. This supersedes the earlier 10.3.1 runtime-compatibility requirement. Preserve persisted-data compatibility and recovery evidence. Optional #283/#284 remain deferred.

Problem

Orleans dotnet/orleans#11155, included in 10.4.0, makes sequence-token equality and ordering depend on a compatibility domain. Derived token types are isolated by default. The two built-in Event Hubs token versions opt into the Event Hubs domain.

OM's EnrichedEventHubSequenceToken : EventHubSequenceTokenV2 does not declare this domain. After upgrading, enriched tokens compare with their own concrete type but cease to compare/equal built-in Event Hubs tokens. This affects stored checkpoints and transitions between standard and enriched adapters, and prevents the provider's historical-token recovery normalization from recognizing enriched tokens.

Work

• Explicitly opt the enriched token into the Event Hubs numeric domain, using the protected SequenceTokenCompatibilityDomain override returning typeof(EventHubSequenceToken), as upstream's custom-token tests do.
• Check enriched adapter cache positions, delivered per-event positions, persisted checkpoints and StreamManager resume against 10.4's provider recovery behavior.
• Exercise the new inherited CreateSequenceTokenForEvent behavior: it now preserves concrete type and metadata via cloning. Retain the enriched batch wrapper's existing custom-container/null-token behavior.
• Preserve JSON discriminator and Orleans serialization identities. Provider/full StreamId remain the checkpoint identity; token compatibility alone does not make positions from different streams interchangeable.

Acceptance

• Enriched, EventHubSequenceToken and EventHubSequenceTokenV2 tokens have symmetric equality/ordering and equal hashes at equal numeric positions; sequence number precedes event index.
• Unrelated provider tokens remain incompatible. Public equality with generic EventSequenceToken stays distinct from the provider's special recovery normalization.
• Historical exact EventSequenceToken V1 checkpoints recover through the actual 10.4 cache/handshake paths where upstream supports them; do not broaden that rule to arbitrary V2/generic tokens.
• Per-event tokens retain offset, enqueue time, provider name and traceparent, including inherited factory use and wrapped custom containers.
• Persisted standard/enriched checkpoint fixtures and provider-qualified tracker resume are covered, along with a genuine cache miss for an evicted position.
• Event Hubs Release tests pass without warnings on 10.4.

This is a compatibility prerequisite for the Orleans 10.4 dependency upgrade #285.

Reviewed against OM source at 2b5d24614ff08a9028ebc61995308176dbb90841; current main at fcca835c3141ac32874c70f687583d2c49ae4847 differs only in OM's version file.