refactor(core): restructured tool output handling with metadata tracking system

- Added output-utils module with tail buffer and artifact allocation helpers.
- Added tool-result module for standardized tool result construction with metadata.
- Replaced inline output truncation with structured metadata system across all tools.
- Updated executors to track detailed output statistics instead of full file paths.
- Standardized artifact storage using pre-allocated paths instead of inline writing.

packages/coding-agent/test/tools/python-execution.test.ts

@@ -33,6 +33,10 @@ describe("python tool execution", () => {
 			exitCode: 0,
 			cancelled: false,
 			truncated: false,
+			totalLines: 1,
+			totalBytes: 2,
+			outputLines: 1,
+			outputBytes: 2,
 			displayOutputs: [],
 			stdinRequested: false,
 		});