[feature](function) Support nanosecond precision for TIMEV2

[jacktengg]

Issue Number: None

Related PR: None

Problem Summary: Commit 23c83f48bceae6578b55dcfe9cae476b9c15fc8a added TIMESTAMP_NS with 9 fractional digits, but TIMEV2 was capped at scale 6 and time functions converted values through integral microseconds. This truncated submicrosecond results such as TIMEDIFF(TIMESTAMP_NS, TIMESTAMP_NS). Extend TIMEV2 to scale 9 while retaining its existing double microsecond-unit representation, and preserve exact nanoseconds in differences, conversions, formatting, constant folding, external TIME readers, arithmetic, and binary query results.

TIMEV2 supports scales up to 9, and time results such as TIMEDIFF on TIMESTAMP_NS preserve nanosecond precision.

• Test: Unit Test and Regression Test
  • ASAN BE and FE builds passed
  • 26 targeted BE unit tests passed
  • 108 targeted FE unit tests passed
  • Relevant timestamp_ns, TIME function, scalar function, binary protocol, and documentation regression suites passed
• Behavior changed: Yes (TIMEV2 supports nanosecond precision)
• Does this need documentation: No

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

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