refactor: resolve timezone-related python 3.12 deprecations

[jsstevenson]

close #127

• remove two cases of timezone-related deprecations -- one regarding default sqlite3 management of time type conversions back into python, and another from the utcnow() method

I'd appreciate some input about where to register the sqlite3 timestamp converter -- I put it in seqaliasdb.py since that seems like the place where it's most important to be pulling out precisely formatted strings but wasn't totally sure. It's sort of weird that the sqlite3 module has you register these things to some global context (?) rather than individual connections.