[FEATURE] Support time zone Information in timestamp literals

Is your feature request related to a problem?
Currently, the query engine does not support time zone information in timestamp literals. When using an ISO 8601 format with a time zone (e.g., 2025-05-15T10:30:00.000Z), the query fails with a SemanticCheckException.

POST {{baseUrl}}/_plugins/_ppl
Content-Type: application/x-ndjson

{
  "query": "source=test00001 | eval t=TIMESTAMP('2025-05-15T10:30:00.000Z')"
}

### Results
{
  "error": {
    "reason": "Invalid Query",
    "details": "timestamp:2025-05-15T10:30:00.000Z in unsupported format, please use 'yyyy-MM-dd HH:mm:ss[.SSSSSSSSS]'",
    "type": "SemanticCheckException"
  },
  "status": 400
}

What solution would you like?
The engine should support ISO 8601 timestamp literals with time zone information (e.g., Z, +08:00, etc.) and interpret them correctly.

What alternatives have you considered?
n/a

Do you have any additional context?
n/a

Start by reproducing the provided PPL request and tracing how TIMESTAMP literals are parsed and validated in the query engine. Check the existing timestamp format handling, then add coverage for Z and offset forms such as +08:00; done means valid ISO 8601 values are accepted and interpreted correctly without breaking existing formats.