Thank you for working on this! ASN.1 time is extremely liberal and this PR currently doesn't consider some corner cases, where it silently drops information.

Please check the specification for details: https://www.itu.int/rec/T-REC-X.680-202102-I

I noticed ASN.1 GeneralizedTime allows higher precision than microseconds. Time in current versions of Ruby is based on Rational, so it should be able to accurately represent any value.

GeneralizedTime supports "fractional minutes/hours", for example, 201612081934.5Z is equivalent to 20161208193430Z. I've never seen this used in the wild and I doubt if it's worth implementing, but there should be an exception if we don't support it.

Comma instead of period may be used as the decimal separator. This doesn't seem supported by ASN1_TIME_to_tm() and would already result in an ASN1Error. I think this is fine. I want a test case to check this behavior.