Convert scontextLog, usageHistory, burnerSubscription, burnerContacts to LAVA @artifact_processor

[abrignoni]

Converts four more parsers to the LAVA @artifact_processor pattern.

• scontextLog — starttime/stoptime selected raw and converted to aware UTC (replacing SQL datetime(...,'UNIXEPOCH')); both marked datetime, preserving the >0 guard.
• usageHistory — lrt converted from epoch-ms to aware UTC (replacing utcfromtimestamp); non-numeric/blank values now normalized to '' instead of a stray space; Timestamp marked datetime. Fixed latent E0602 (logfunc was used but never imported — that path is now removed).
• burnerSubscription — creationDate/renewalDate json-extracted raw and converted to aware UTC; Timestamp/Renewal Date marked datetime. Fixed paths (was a bare string, not a 1-tuple → glob iterated char-by-char).
• burnerContacts — flat conversion; Phone Number marked phonenumber; same paths tuple fix.

Verified: byte-compile, decorated 4-arg signature, returns 3-tuple, output_types valid, paths are tuples, loader resolves, pylint (W1514/unused/errors) clean.