Revamp `Gate` introduce `ConductanceSystem`

[vi-hart]

Gate can accept any AbstractSystem allowing for overloading of functions like IonChannel or _conductance. The Generator for Gate uses a ReactionSystem and allows for simple conversion to other system types through optional kwargs.

[wsphillips]

rebased onto main to pull in recent patches, tests, and dependency updates. I'll start reviewing the changes next

[wsphillips]

Still not done, but the idea is to continue implementing overloads to satisfy the AbstractSystem interface next.

Then, in channel construction we can do something roughly like...

kinetics = merge(mgate, hgate)
wrap = ODESystem([g ~ gbar * mgate.transform(mgate.output) * ... etc], name = :NaV)
channel = extend(wrap, convert(ODESystem, kinetics))

[vi-hart]

Implemented basic macros for generating gates and ion channels. It may break while reworking gates and ion channels, but is a start/template for later.

# p defaults to 1
@gate h begin
    α = 0.07*exp(-(Vₘ + 65)/20)
    β = 1/(1 + exp(-(Vₘ + 35)/10))
end

# a gate can be generated with a unique variable name
@gate begin
    α = 0.07*exp(-(Vₘ + 65)/20)
    β = 1/(1 + exp(-(Vₘ + 35)/10))
end

# support for additional parameters (ie. vshift)
@gate m begin
    α = 0.1*(Vₘ + 40 - vshift)/(1 - exp(-(Vₘ + 40)/10))
    β = 4*exp(-(Vₘ + 65)/18)
end p = 3

# order of the rate equations doesn't matter
@gate m begin
    β = 4*exp(-(Vₘ + 65)/18)
    α = 0.1*(Vₘ + 40)/(1 - exp(-(Vₘ + 40)/10))
end p = 3

# gate macros can be nested inside an ionchannel macro
NaV = @ionchannel NaV{Sodium} begin
    @gate m begin
        α = 0.1*(Vₘ + 40)/(1 - exp(-(Vₘ + 40)/10))
        β = 4*exp(-(Vₘ + 65)/18)
    end p = 3
    @gate h begin
        α = 0.07*exp(-(Vₘ + 65)/20)
        β = 1/(1 + exp(-(Vₘ + 35)/10))
    end
end gbar = 100mS/cm^2

[wsphillips]

@pjh6654 Nice start! The macro work should really live in a separate PR though. Even though there's more to do here and tests aren't passing, I'm going to merge what we have so far to main so that dividing up the additional work is less complicated.