Pydantic can be installed without binary files. This significantly
reduces the additional size it adds to the compressed Lambda packages
(down to 2MB from 25MB) at the expense of 30%-50% of its performance.

While at it I also updated the amount of megabyte Pydantic adds to the
package, as it wasn't clear if the stated number referred to compressed
or uncompressed package size and I couldn't reproduce the 75MB either
way.