Updates for Python 3.12 compatibility (SYN-6184)

[vEpiphyte]

• Replace utcfromtimestamp with fromtimestamp Deprecate utcnow and utcfromtimestamp python/cpython#103857
• s_common.chunks Can raise a KeyError when trying to chunk a dictionary slice not hashable python/cpython#84783
• link.fromspawn cannot be called from the interpreter / ioloop that created the original link asyncio.StreamReader.read hangs for reused socket file descriptors when asyncio.StreamWriter.close() is not called python/cpython#88968

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (573a012) 97.30% compared to head (ce6ed8c) 97.20%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3355      +/-   ##
==========================================
- Coverage   97.30%   97.20%   -0.11%     
==========================================
  Files         228      228              
  Lines       46690    46691       +1     
==========================================
- Hits        45431    45384      -47     
- Misses       1259     1307      +48     

Flag	Coverage Δ
linux	97.20% <100.00%> (-0.01%)	⬇️
linux_replay	?

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Files	Coverage Δ
synapse/cmds/cron.py	97.72% <100.00%> (ø)
synapse/lib/stormlib/stix.py	98.28% <100.00%> (+<0.01%)	⬆️
synapse/lib/stormtypes.py	98.76% <100.00%> (ø)

... and 10 files with indirect coverage changes

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