feat: add timestamp option to debug

[rejunp]

Summary

This PR adds support for a timestamp option in Mongoose debug object configuration.

With this change, users can enable timestamped debug output while preserving Mongoose’s built-in formatting:

mongoose.set('debug', { timestamp: true });

Example output:

[2026-04-02T10:00:00.000Z] Mongoose: users.findOne({}, {})

Motivation

Mongoose debug logs are useful for understanding executed operations, but they currently lack per-line time context unless users implement a custom debug function.
This adds a built-in, low-friction option for timestamped output without requiring users to reimplement formatter logic.

What changed

• Added debug.timestamp support in console debug output path.
• Timestamp format is ISO 8601 and wrapped in square brackets.
• Kept stream debug behavior unchanged.
• Updated TypeScript option definitions to include timestamp?: boolean.
• Added/updated tests for debug timestamp behavior.
• Updated docs for Mongoose.prototype.set() debug option and FAQ examples.

Scope / Behavior

• Applies to object-style debug config ({ timestamp: true }).
• Applies to console debug output.
• Does not add duration/performance timing.
• Does not modify stream debug output.

Backward compatibility

• Existing debug behavior is unchanged unless timestamp: true is explicitly set.
• No breaking API changes.

Linked issue

Resolves #16215

Validation

• Focused runtime debug test for timestamp output passes.
• Type tests pass.