Extract connector runtime snapshot management (#32698)

## What changed

- Move the Codex Apps tool cache into a reusable `codex-connectors` runtime manager keyed by account and workspace.
- Represent cached tools as atomically published snapshots with refresh timestamps while preserving the newest accepted fetch generation.
- Harden disk persistence with bounded reads, atomic file replacement, and serialized writes so an older fetch cannot overwrite newer state.

## Testing

Add coverage for identity isolation, snapshot timestamps, oversized cache files, atomic replacement, and concurrent persistence ordering.

GitOrigin-RevId: 5ea2234469daae3abf54b030244c3251de62ca5a

codex-rs/codex-mcp/src/tools.rs

@@ -19,9 +19,6 @@ use tracing::warn;
 
 use crate::mcp::sanitize_responses_api_tool_name;
 
-pub(crate) const MCP_TOOLS_CACHE_WRITE_DURATION_METRIC: &str =
-    "codex.mcp.tools.cache_write.duration_ms";
-
 const LEGACY_MCP_TOOL_NAME_PREFIX: &str = "mcp__";
 
 #[derive(Debug, Clone, Serialize, Deserialize)]