(core) Update logging in sandbox code, and log tracebacks as single log messages.

Summary:
- Replace logger module by the standard module 'logging'.
- When a log message from the sandbox includes newlines (e.g. for tracebacks),
  keep those lines together in the Node log message.

  Previously each line was a different message, making it difficult to view
  tracebacks, particularly in prod where each line becomes a separate message
  object.

- Fix assorted lint errors.

Test Plan: Added a test for the log-line splitting and escaping logic.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3956

app/server/lib/NSandbox.ts

@@ -279,7 +279,7 @@ export class NSandbox implements ISandbox {
     if (!this._streamToSandbox) {
       throw new Error('expected streamToSandbox to be configured');
     }
-    const sandboxStderrLogger = sandboxUtil.makeLinePrefixer('Sandbox stderr: ', this._logMeta);
+    const sandboxStderrLogger = sandboxUtil.makeLogLinePrefixer('Sandbox stderr: ', this._logMeta);
     this.childProc.stderr!.on('data', data => {
       this._lastStderr = data;
       sandboxStderrLogger(data);