Cosmos: public RID addressing API (ResourceId/ResourceIdentity) (3/3)

[simorenoh]

Slice 3 of 3 (stacked on PR #4663) for epic #4637.

This final slice adds the SDK-facing public API in azure_data_cosmos for addressing Cosmos databases and containers by name or RID. No driver changes — it builds on the driver surface landed in slices 1 and 2.

What's added

• ResourceId / ResourceIdentity — new public types. ResourceId wraps a RID (Cow<'static, str>, const from_static, Display, AsRef, From<&str|String|&String>). ResourceIdentity is a #[non_exhaustive] enum (Name | Rid) with From conversions so a &str/String selects name addressing and a ResourceId selects RID addressing.
• Name-or-RID clients — CosmosClient::database_client and DatabaseClient::container_client now take impl Into. DatabaseClient gains
  ame()/
  id(), and id() now returns &ResourceIdentity.
• Addressing guards — RID-addressed containers resolve through the driver's
  esolve_container_by_rid with a parent-database cross-check (CLIENT_INVALID_RESOURCE_ID when the resolved container's parent DB doesn't match the addressed database). Mixing name and RID across the DB/container hierarchy is rejected with CLIENT_MIXED_NAME_RID_ADDRESSING.
• Throughput fast path — RID-addressed throughput reads/replaces reuse the RID directly and skip the extra database read (shared
  esource_id() helper).

Testing

• 6 new
  esource_identity unit tests (run in CI).
• New emulator e2e test cosmos_rid_addressing.rs — compile-verified in CI; runs under the emulator.

Breaking changes

• database_client/container_client take impl Into instead of &str (deref call sites need &*value/.as_ref()).
• DatabaseClient::id() now returns &ResourceIdentity instead of &str.

Base is targeted at simorenoh/cosmos-rid-slice2-resolution so the diff is reviewable in isolation.