fix(obs-studio): reject non-finite geometry in source transforms (#397)

* fix(obs-studio): reject non-finite geometry in position/size/crop

validate_position accepted NaN coordinates into project JSON. size/crop
converted NaN via int() with a cryptic error. Reject non-finite values
up front, matching validate_range.

* test(obs-studio): drop unused math import in geometry nan tests

* fix(obs-studio): wire finite geometry checks into source transforms

validate_position/size/crop were unused while add_source and
transform_source accepted NaN into project JSON. Call the validators
from those paths and cover the live transform entrypoint.

* fix(obs-studio): validate finite geometry without float-rounding ints

* test(obs-studio): preserve large integers in geometry validators

* fix(obs-studio): preserve decimal integer geometry

* test(obs-studio): document integer string regressions

* fix(obs-studio): validate integer geometry and make source transform validation atomic