Package can create invalid Ulids

[Flohack74]

Hi,

as the Ulid specification excludes letters I L O U (Crockford's base32) I made a small test to see how its implemented here. For example a TryParse of invalid 01ARZ3NDEITSV4RRFFQ69G5FAV (note the I) leads to an invalid Ulid value of 01ARZ3NDFZTSV4RRFFQ69G5FAV, without error.

Is there a reason for skipping validity checks, mainly for speed reason?

Thanks!