Towards Julia v1.9

[icweaver]

Just opening this to track potential reasons for bumping our minimum supported Julia version from v1.6 to at least v1.9:

• Julia v1.10.8 is now the current LTS
• Package extensions require at least v1.9. This would be useful for Doc plots with Makie #58
• Base.@kwdef is now exported in v1.9. This would remove our Parameters.@with_kw dependency. Note: would need to work around @assert not being supported in Base.@kwdef, so probs not worth the hassle. Related discussion
  • Actually, maybe not that bad? Replace Parameters.@with_kw with Base.@kwdef #61