Make MCP and Code Mode input schema budgets configurable (#47936)

## Why

Fixed schema budgets can strip parameter descriptions from large MCP tools or render their Code Mode input types as `unknown`. Allow larger budgets to preserve that guidance.

## What changed

- Add `mcp_servers.<name>.tool_input_schema_max_bytes` to configure the UTF-8 byte threshold for best-effort input schema compaction, retaining the 5,000-byte default.
- Add `features.code_mode.tool_input_schema_max_bytes` for rendered input types. Use the largest of the 16,000-byte default, the Code Mode setting, and the ordinary MCP server's explicit setting.
- Apply rendering budgets to prompt declarations and the runtime tool catalog, and avoid reusing cached declarations after the Code Mode budget changes.

## Testing

Add coverage for UTF-8 compaction thresholds, budget precedence, configuration round trips, and preservation of parameter guidance in both the Code Mode prompt and `ALL_TOOLS`.

GitOrigin-RevId: 0ef2823a614d4794e636f518b09c0b03a5239b45

codex-rs/code-mode/src/grpc_session/conversion_tests.rs

@@ -28,6 +28,7 @@ fn execute_request_preserves_tool_schemas_namespaces_and_limits() {
             description: "search the workspace".to_string(),
             kind: CodeModeToolKind::Freeform,
             input_schema: Some(json!({"type": "object"})),
+            input_schema_max_bytes: None,
             output_schema: Some(json!({"type": "string"})),
         }],
         source: "text('hello')".to_string(),