Slice 3/6 of the postcode_splitter refactor (Hestia-Homes/Model#1101).
Introduces a thin typed infrastructure layer wrapping boto3 for the AWS
side of the splitter. S3Client/SqsClient are bucket-/queue-bound byte
adapters; CsvS3Client subclasses S3Client to round-trip CSV row dicts
via the existing parse_s3_uri helper in utils/s3.py; Address2UprnQueueClient
subclasses SqsClient to publish the typed {task_id, sub_task_id, s3_uri}
fan-out body the downstream consumer expects. moto[s3,sqs] is pulled into
test.requirements.txt and the new tests/infrastructure/ suite exercises
each client against the moto backend (S3 round-trip, CSV round-trip,
SQS send + body inspection, typed publish + body inspection). pyright
--strict is clean on the new modules.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
