[Cosmos] Audit RxDocumentServiceRequest.clone() for missing field copies

[jeet1995]

Problem

RxDocumentServiceRequest.clone() does not copy all fields. This was discovered during PR #48432 where partitionKeyDefinition was missing from the clone, causing NPE in hedged thin client queries.

A field-by-field audit reveals ~12 other fields that are not copied by clone():

• effectivePartitionKey
• properties (carries excludedRegions and request-scoped metadata)
• throughputControlGroupName
• responseTimeout
• entityId
• and others

Impact

For hedging scenarios (where clone() is used), the cloned request silently loses these properties. The properties map is particularly concerning since it carries excludedRegions -- a hedged request could target an excluded region.

Proposed Fix

1. Audit every field in RxDocumentServiceRequest against clone()
2. Add missing field copies
3. Add a reflection-based completeness test that fails when a new field is added to the class but not included in clone() -- this prevents future regressions

Context

• Reported in PR #48432 review by @xinlian12
• Related to [GATEWAY V2] thin client availability strategy work
• clone() is a maintenance trap -- every new field silently breaks hedging until someone discovers a bug
• The reflection-based test would make this self-enforcing