[C++][Gandiva] castVARCHAR_timestamp_int64 produces negative milliseconds for pre-epoch timestamps (before 1970-01-01)

[dmitry-chirkov-dremio]

Describe the bug, including details regarding any error messages, version, and platform.

castVARCHAR_timestamp_int64 produces negative milliseconds for pre-epoch timestamps (before 1970-01-01).

Example: 0107-10-17 12:20:03.900 → "0107-10-17 12:20:03.-10"
Cause: in % MILLIS_IN_SEC returns negative values for negative timestamps.
Fix: Use EpochTimePoint::TimeOfDay().subseconds().count() for correct millisecond extraction.

Failing Tests (before fix)

    ts = StringToTimestamp("67-5-1 00:00:04") + 920;
    out = castVARCHAR_timestamp_int64(context_ptr, ts, 24L, &out_len);
    EXPECT_EQ(std::string(out, out_len), "0067-05-01 00:00:04.920");
    // Actual: "0067-05-01 00:00:04.-80"

Component(s)

C++, Gandiva

[dmitry-chirkov-dremio]

take