Contract tests for tools/fal_common.py: queue-URL normalization
(trailing slash / whitespace / empty-raises), _extract_http_status
response-vs-exc precedence and non-int rejection, the
_ManagedFalSyncClient RuntimeError guards against fal_client private
API drift, and submit()'s queue-URL + POST/json/timeout wiring.
Trimmed on landing: test_non_string_coerced_to_string (pins an
implementation accident, not a contract) per the coverage-padding
policy in AGENTS.md.
Salvaged from #52166.
