TextFormatUtil.writeTimestamp writes a value with a decimal point but the spec specifies an int64 #1277
Description
static void writeTimestamp(Writer writer, long timestampMs) throws IOException {
writer.write(Long.toString(timestampMs / 1000L));
writer.write(".");
Writes a decimal point.
The spec https://prometheus.io/docs/instrumenting/exposition_formats/#text-format-details
specifies the timestamp as an int64
The timestamp is an int64 (milliseconds since epoch, i.e. 1970-01-01 00:00:00 UTC, excluding leap seconds), represented as required by Go's [ParseInt()](https://golang.org/pkg/strconv/#ParseInt) function.
This causes Prometheus/promtool to error on metrics with a timestamp
error while linting: text format parsing error in line 17: expected integer as timestamp, got "1739889638.000"