Simplify tool executor and registry plumbing (#22636)

## Why

The tool runtime path still had a typed output associated type on
`ToolExecutor`, plus a core-only `RegisteredTool` adapter and
extension-only executor aliases. That made every new shared tool runtime
carry extra adapter plumbing before it could participate in core
dispatch, extension tools, hook payloads, telemetry, and model-visible
spec generation.

This PR moves output erasure to the shared executor boundary so core and
extension tools can use the same execution contract directly.

## What Changed

- Changed `codex_tools::ToolExecutor` to return `Box<dyn ToolOutput>`
instead of an associated `Output` type.
- Removed the extension-specific `ExtensionToolExecutor` /
`ExtensionToolOutput` aliases and exposed `ToolExecutor<ToolCall>` plus
`ToolOutput` through `codex-extension-api`.
- Reworked core tool registration around `CoreToolRuntime` and
`ToolRegistry::from_tools`, removing the extra `RegisteredTool` /
`ToolRegistryBuilder` layer.
- Consolidated model-visible spec planning and registry construction in
`core/src/tools/spec_plan.rs`, including deferred tool search and
code-mode-only filtering.
- Added `ToolOutput` helpers for post-tool-use hook ids and inputs so
MCP, unified exec, extension, and other boxed outputs preserve the same
hook payload behavior.
- Updated core handlers, memories tools, and the related
registry/spec/router tests to use the simplified contract.

## Test Coverage

- Updated coverage for tool spec planning, registry lookup, deferred
tool search registration, extension tool routing, post-tool-use hook
payloads, dispatch tracing, guardian output extraction, and memories
extension tool execution.

codex-rs/ext/extension-api/src/contributors.rs

@@ -4,12 +4,13 @@ use std::sync::Arc;
 use codex_protocol::items::TurnItem;
 use codex_protocol::protocol::ReviewDecision;
 use codex_protocol::protocol::TokenUsageInfo;
+use codex_tools::ToolCall;
+use codex_tools::ToolExecutor;
 
 use crate::ExtensionData;
 
 mod prompt;
 mod thread_lifecycle;
-mod tools;
 mod turn_lifecycle;
 
 pub use prompt::PromptFragment;
@@ -17,8 +18,6 @@ pub use prompt::PromptSlot;
 pub use thread_lifecycle::ThreadResumeInput;
 pub use thread_lifecycle::ThreadStartInput;
 pub use thread_lifecycle::ThreadStopInput;
-pub use tools::ExtensionToolExecutor;
-pub use tools::ExtensionToolOutput;
 pub use turn_lifecycle::TurnAbortInput;
 pub use turn_lifecycle::TurnStartInput;
 pub use turn_lifecycle::TurnStopInput;
@@ -106,7 +105,7 @@ pub trait ToolContributor: Send + Sync {
         &self,
         session_store: &ExtensionData,
         thread_store: &ExtensionData,
-    ) -> Vec<Arc<dyn ExtensionToolExecutor>>;
+    ) -> Vec<Arc<dyn ToolExecutor<ToolCall>>>;
 }
 
 /// Future returned by one claimed approval-review contribution.