Release 4.0-beta9

New features:

• allow "var1 ~ dist1; var2 ~ dist2; model(var1, var2)" in the command-line language
• non-reversible substitution models for fixed alignments (and for variable-alignments in the next pre-release)
• add Mac/ARM builds.

Fixes:

• fix quotes and _ in Nexus names
• fix numeric alphabets (e.g 0/1 characters)
• fix crash with long sequences
• fix crash in meson test