LOGC-46: Fix DateTime64 millisecond truncation in LogFetcher

[dvasilas]

This substitutes #90 with a much simpler fix.

The issue is that the ClickHouse Go driver truncates milliseconds when binding time.Time to DateTime64(3) parameters.
I wrote a simple script that reproduces the issue
With the following table:

CREATE TABLE %s (
             id        String,
             startTime DateTime64(3)
) ENGINE = MergeTree() ORDER BY startTime

when we insert with

records := []struct {
        id        string
        startTime time.Time
    }{
        {"rec1", time.Date(2026, 1, 20, 16, 20, 36, 5*int(time.Millisecond), time.UTC)},   // 36.005s
        {"rec2", time.Date(2026, 1, 20, 16, 20, 36, 54*int(time.Millisecond), time.UTC)},  // 36.054s - THE OFFSET
        {"rec3", time.Date(2026, 1, 20, 16, 20, 36, 100*int(time.Millisecond), time.UTC)}, // 36.100s
    }

    for _, rec := range records {
        err := conn.Exec(ctx, fmt.Sprintf("INSERT INTO %s VALUES (?, ?)", tableName), rec.id, rec.startTime)
        if err != nil {
            t.Fatalf("failed to insert %s: %v", rec.id, err)
        }
    }

we get

docker exec workbench-clickhouse-shard-1 clickhouse-client --port 9002 -q "SELECT * FROM datetime64_test_1769182943901284695"
rec2    2026-01-20 16:20:36.000
rec3    2026-01-20 16:20:36.000
rec1    2026-01-20 16:20:36.000

but when we also insert

nowStr := fmt.Sprintf("%.3f", float64(time.Now().UnixMilli())/1000.0)
t.Logf("Inserting rec_str with timestamp string: %s", nowStr)
err = conn.Exec(ctx, fmt.Sprintf("INSERT INTO %s VALUES (?, ?)", tableName), "rec_str", nowStr)

we get

rec1    2026-01-20 16:20:36.000
rec2    2026-01-20 16:20:36.000
rec3    2026-01-20 16:20:36.000
rec_now 2026-01-23 15:52:48.000
rec_str 2026-01-23 15:52:48.815

The fix is to apply this conversion to log-courier