[FEATURE] Support switching between non-coercible types via drop/add

[aleclarson]

Describe the bug

Incompatible cast does not result in DROP COLUMN followed by ADD COLUMN.

This is occurring for me with all hazards allowed and plan validation disabled.

Error: executing migration statement. the database maybe be in a dirty state: 
{ALTER TABLE "public"."activity" ALTER COLUMN "ts" SET DATA TYPE timestamp with 
time zone using "ts"::timestamp with time zone 3s 3s 
[ACQUIRES_ACCESS_EXCLUSIVE_LOCK: This will completely lock the table while the data 
is being re-written. The duration of this conversion depends on if the type conversion 
is trivial or not. A non-trivial conversion will require a table rewrite. A trivial 
conversion is one where the binary values are coercible and the column contents are not 
changing.]}: 
ERROR: cannot cast type integer to timestamp with time zone (SQLSTATE 42846)

Expected behavior

DROP then ADD

To Reproduce

Change a column type from integer to timestamptz.

Context pg-schema-diff version: 5fe8259b82bd784644224a861cce575339a45a59 pg-schema-diff usage: CLI Postgres version: 14

[bplunkett-stripe]

This isn't so much a bug as it is a limitation. We have not accounted for incompatible types when doing data type migrations. Instead, you will need a schema that removes the column and a schema that adds the column with the new type. I can make this feature request.

[bplunkett-stripe]

Relates to #52 .

Ideally, we have some way that given to two types x and y, we know (1) if they are coercible and (2) the binary is coercible, i.e., does not require a full table scan.