Fix all MxGateway.Client.Rust code-review findings

Resolves Client.Rust-001 through Client.Rust-011.

Build/test/clippy gate (Client.Rust-001/002/003):
- options.rs: doc comments on with_max_grpc_message_bytes /
  max_grpc_message_bytes (#![warn(missing_docs)])
- session.rs: rename BulkReplyKind variants to drop the shared `Bulk`
  suffix (clippy::enum_variant_names)
- galaxy.rs: deref instead of clone on Option<Timestamp>
  (clippy::clone_on_copy — an extra violation the gate also hit)
- mxgw-cli: assert version_json against GATEWAY/WORKER_PROTOCOL_VERSION
  constants instead of the stale literal 2
`cargo clippy --workspace --all-targets -- -D warnings` now passes.

Correctness / error handling:
- version.rs: CLIENT_VERSION = env!("CARGO_PKG_VERSION") (Client.Rust-004)
- session.rs: register/add_item/add_item2 handle extractors and
  bulk_results now return Err(Error::MalformedReply) instead of a
  silent 0 / empty vec on a shapeless OK reply (Client.Rust-005/006)
- error.rs: new Error::Unavailable classifies Code::Unavailable /
  ResourceExhausted as transient (Client.Rust-010)
- session.rs: per-call unique correlation ids via an atomic counter
  (Client.Rust-011)

Other:
- value.rs: MxValue/MxArrayValue compute the projection on demand
  instead of caching it, so a wire-only value pays no projection cost
  (Client.Rust-008)
- RustClientDesign.md: correct the crate layout, drop the unused
  `tracing` dependency (Client.Rust-007)
- client_behavior.rs: tests for the bulk-size cap, a mid-stream status
  fault, and the unreadable-CA-file path (Client.Rust-009)

cargo fmt / test --workspace (27 tests) / clippy all pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

clients/rust/src/version.rs

@@ -3,8 +3,9 @@
 //! The protocol versions track the values the gateway and worker negotiate on
 //! `OpenSession` and let test harnesses cross-check the wire contract.
 
-/// Semantic version of this Rust client crate. Mirrors `Cargo.toml`.
-pub const CLIENT_VERSION: &str = "0.1.0-dev";
+/// Semantic version of this Rust client crate, taken from `Cargo.toml` at
+/// compile time so the two cannot drift.
+pub const CLIENT_VERSION: &str = env!("CARGO_PKG_VERSION");
 
 /// Public gateway gRPC protocol version this client targets.
 pub const GATEWAY_PROTOCOL_VERSION: u32 = 3;