Honour the int64 integer format (#544)

All Swagger integer definitions rendered as F# int regardless of
format, narrowing 64-bit IDs to Int32: overflow on the way out,
rejection of valid responses on the way in. "format": "int64" now
renders as int64 in both defnToType and renderType; other or absent
formats remain int. E.g. IssueGetComments now takes index : int64 and
Team.Id is int64 option.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: Smaug123