Add Rust session store identity support

[gimenete]

Summary

• add public SessionStoreIdentity with canonical authority and account_id fields
• support optional sessionStoreIdentity payloads on session create and resume
• add Client::set_session_store_identity for the server-scoped sessionStore.setIdentity set/clear contract
• cover exact camelCase serialization, omission, and setter/clear wire requests

Validation

• cargo +nightly-2026-04-14 fmt --check
• cargo test --lib session_store_identity
• cargo test --features test-support --test session_test set_session_store_identity
• cargo clippy --all-features --all-targets -- -D warnings

[Copilot]

Copilot review overview

🟡 Changes recommended

The new public struct needs non-exhaustive construction to preserve future API compatibility.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review tier: Balanced
Findings: 1

New issues introduced by this change (1)

Severity	Finding
	rust/​src/​types.rs — This new public struct can be constructed with a literal, so adding any protocol field later would…

What changed in this PR

Adds Rust SDK support for account-scoped session-store identities.

Changes:

• Adds the public identity type and create/resume configuration.
• Implements the set/clear JSON-RPC API.
• Tests serialization and wire requests.

File	Description
rust/​src/​types.rs	Defines identity and configuration support.
rust/​src/​wire.rs	Serializes identity into create/resume payloads.
rust/​src/​lib.rs	Adds the client identity setter.
rust/​tests/​session_test.rs	Verifies set and clear requests.

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