Mikolaj Metto

bigtable: Allow microseconds for TimestampRangeFilter (again)

6

**Is your feature request related to a problem? Please describe.** Could you please remove code rejecting microseconds when defining `TimestampRangeFilter`s? **Describe the solution you'd like** 1. Remove if-block [here](https://github.com/googleapis/google-cloud-go/blob/main/bigtable/bttest/inmem.go#L746-L753) 2....

feat(bigtable): Restored microseconds as timestamp range filter ranges

9

fixes #5931