Incorrect nanosecond values in Firestore date comparison queries

### Operating System

Windows 11

### Environment (if applicable)

Firebase Admin SDK (Node.js backend), Firebase JavaScript SDK (Web frontend), Firebase Console UI (Firestore Database interface)

### Firebase SDK Version

firebase-admin "^13.1.0

### Firebase SDK Product(s)

Firestore

### Project Tooling

Node.js V.22, Express, firebase-admin. But it actually affects Firebase Console UI, and any implementations in React with Firebase JavaScript SDK

### Detailed Problem Description

## Describe the bug
When using .where() queries with date comparison operators (>=, >, <, <=) in Firestore, the generated timestamp has incorrect millisecond values. Instead of using the correct timestamp format (e.g., 2025-10-10T00:00:00.000Z), the query generates timestamps with wrong millisecond precision, resulting in incorrect query results.

## Affected environments:

✅ Firebase Admin SDK (Backend)
✅ Firebase Web SDK (Frontend)
✅ Firebase Console UI (Firestore query interface)

This appears to be a systemic issue affecting all Firebase/Firestore implementations.

### Steps and code to reproduce issue

**Example query**:
```js
// Frontend or Backend
db.collection('myCollection')
.where('marca_de_tiempo', '>=', new Date('2025-10-01T00:00:00.000Z'))
.get()
```
## Expected behavior:
The query should generate a filter with correct timestamp:
```json
{
"fieldPath": "From",
"op": "GREATER_THAN_OR_EQUAL",
"value": {
"timestampValue": "2025-10-01T04:00:00.000000000Z"
}
}
```
## Actual behavior:
The query generates incorrect millisecond values:
```json
{
"fieldPath": "From",
"op": "GREATER_THAN_OR_EQUAL",
"value": {
"timestampValue": "2025-10-01T04:00:00.011000000Z" // Wrong!
}
}
```
Note the incorrect milliseconds: 011000000 instead of 000000000

## Evidence
See attached screenshot showing the Network tab in Chrome DevTools where the `structuredAggregationQuery` request clearly shows the malformed timestamp in the `compositeFilter` section.

**Key observations from screenshot**:
- Input date: 1 oct 2025 at 00:00:00
- Expected nanoseconds: 000000000
- Actual nanoseconds: 011000000Z ❌

## Impact
-Queries return incorrect results:
- Date range filters fail to work as expected
- Data consistency issues across the application
- Affects production systems using date-based queries

This affects specially reporting when data is aggregated in a hourly or daily basis.

## Environment details

- Firebase Console: Cloud Firestore Database UI
- Browser: Chrome (DevTools visible in screenshot)
- SDKs affected: firebase-admin (Node.js backend) and Firebase Web SDK

## Expected fix
Firestore queries should correctly serialize date/timestamp values in the where() clause with proper millisecond/nanosecond precision: 000000000 for midnight, or the exact value provided by the Date object.