Incorrect default cast from MSSQL `int` (auto-increment) to PG `bigserial`

[nathanael-ruf]

int is 4 bytes in mssql: https://learn.microsoft.com/en-us/sql/t-sql/data-types/int-bigint-smallint-and-tinyint-transact-sql?view=sql-server-ver16 bigserial is 8 bytes: https://www.postgresql.org/docs/current/datatype-numeric.html

Expected: pgloader converts to serial (4 bytes).

Besides just more space this has implications for node applications using the pg library which returns strings instead of numbers because numbers in js can't represent full 64bit integers.

Location in the code: https://github.com/dimitri/pgloader/blob/29afa9de0563b25bf2da3a9b2d84e2b1b25de098/src/sources/mssql/mssql-cast-rules.lisp#L15-L16

(related: #1586. I only found this issue after applying the fix of #1586 on a fork)