chore: move mcp-server/src/wire_format.rs to protocol/src/mcp_protocol.rs (#2423)

The existing `wire_format.rs` should share more types with the
`codex-protocol` crate (like `AskForApproval` instead of maintaining a
parallel `CodexToolCallApprovalPolicy` enum), so this PR moves
`wire_format.rs` into `codex-protocol`, renaming it as
`mcp-protocol.rs`. We also de-dupe types, where appropriate.

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* #2424
* __->__ #2423

codex-rs/protocol/src/lib.rs

@@ -1,4 +1,5 @@
 pub mod config_types;
+pub mod mcp_protocol;
 pub mod message_history;
 pub mod parse_command;
 pub mod plan_tool;