NIFI-15305 Fix PutDatabaseRecord Timestamp Parsing

[taylorobyen]

Summary

NIFI-15305 Fixes PutDatabaseRecord's inconsistent timestamp parsing when handling epoch timestamps.

Epoch timestamps are supposed to be in milliseconds, but when fractional milliseconds are included in the timestamp it is incorrectly handled as seconds resulting in dates very far in the future.

Behavior prior to my patch:
Correct handling of a timestamp with only whole milliseconds:

{"ts": 1765056655230}

Timestamp loaded into PostgreSQL: 2025-12-06 16:30:55.230 -0500 ✅

Incorrect handling of a timestamp that includes fractional milliseconds:

{"ts": 1765056655230.746}

Timestamp loaded into PostgreSQL: 57902-06-03 07:20:30746. -0400 ❌

This bug was introduced in #8332, which was trying to allow for microsecond precision for epoch timestamps. Before #8332, the fractional milliseconds were truncated as the timestamp was always converted from String to long.

My implementation allows for microsecond precision while handling all epoch timestamps as milliseconds.

Tracking

Please complete the following tracking steps prior to pull request creation.

Issue Tracking

• Apache NiFi Jira issue created

Pull Request Tracking

• Pull Request title starts with Apache NiFi Jira issue number, such as NIFI-00000
• Pull Request commit message starts with Apache NiFi Jira issue number, as such NIFI-00000

Pull Request Formatting

• Pull Request based on current revision of the main branch
• Pull Request refers to a feature branch with one commit containing changes

Verification

Please indicate the verification steps performed prior to pull request creation.

Build

• Build completed using ./mvnw clean install -P contrib-check
  • JDK 21
  • JDK 25

Licensing

• New dependencies are compatible with the Apache License 2.0 according to the License Policy
• New dependencies are documented in applicable LICENSE and NOTICE files

Documentation

• Documentation formatting appears as expected in rendered files