SFAz3 models seem to have max length 21 characters

[jsboige]

A simple repro: In Automata.Z3.Tests in FiniteAutomataTests.cs#L510, change \d{3} for \d{22} and the test should fail with a valid string truncated for the first 21 chars.

Tests with other longer repetitions yielded the same behavior.

Furthermore, trying to upgrade Z3 NuGet dependency from 4.5 to version 4.8.1, (more recent versions don't seem to like the targeted Framework 4.5), a couple tests won't pass anymore. The one above then fails with an empty model.