Turns out the 32bit tests were actually using 64bit Godot and testing
the 64bit binaries.
This commit ensures that the tests use the correct builds and adds
32bit linux to the gdextension file.
Adds additional tests for the interface. Creates a new base test class
GodotXtermTest that adds some additional assert methods. Tests
inheriting from this should override the got_described_class() method.
Add instance of the described class named 'subject' will be created and
added to the scene tree before each test.
Adds the option `use_threads` to PTY (enabled by default) which improves
performance when enabled. For example, running `time cat file.txt` where
file is ~4.5MB will take ~0.250s with threads enabled, versus >20s when
disabled.
