refactor snapshot creation and check trace data against snapshot

[nick-gorman]

• snapshot definition is moved to the translator
• conversion to 'ns' datetime units for traces is moved to the translator
• functionality added to check traces against snapshot before they are saved by the translator
• Also changes config structure so all config inputs related to temporality sit under the 'temporal' key

[codecov]

Codecov Report

Attention: Patch coverage is 79.66102% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/ispypsa/config/validators.py	53.84%	3 Missing and 3 partials ⚠️
src/ispypsa/translator/buses.py	33.33%	2 Missing ⚠️
src/ispypsa/translator/generators.py	33.33%	2 Missing ⚠️
src/ispypsa/translator/time_series_checker.py	87.50%	0 Missing and 2 partials ⚠️

Files with missing lines	Coverage Δ
src/ispypsa/model/buses.py	35.71% <ø> (+2.38%)	⬆️
src/ispypsa/model/generators.py	26.08% <ø> (+1.08%)	⬆️
src/ispypsa/model/initialise.py	100.00% <100.00%> (+68.75%)	⬆️
src/ispypsa/translator/snapshot.py	100.00% <100.00%> (ø)
src/ispypsa/translator/buses.py	20.00% <33.33%> (+1.08%)	⬆️
src/ispypsa/translator/generators.py	23.52% <33.33%> (+0.94%)	⬆️
src/ispypsa/translator/time_series_checker.py	87.50% <87.50%> (ø)
src/ispypsa/config/validators.py	81.13% <53.84%> (ø)

... and 5 files with indirect coverage changes

[prakaa]

Look good @nick-gorman, minor renaming suggestions only