Full system balancing

[TorkelE]

Creates a function balance_system, which takes a ReactionSystem and returns a version with all its reactions balanced.

rs = @reaction_network begin
    @species C(t) O(t) H(t)
    @compounds begin
        H2(t) = 2H
        CH4(t) = C + 4H
        O2(t) = 2O
        CO2(t) = C + 2O
        H2O(t) = 2H + O
    end
    1.0, C + H2 --> CH4
    2.0, CH4 + O2 --> CO2 + H2O
end
rs_balanced = balance_system(rs)

[TorkelE]

I was unsure how to actually construct a proper reaction from the base. Had a look at some outputs but didn't really understand. At some point we should support it, but not really a priority.

[TorkelE]

Although we probably could raise a issue that it should be fixed

[isaacsas]

We should probably update these error messages as they are imprecise (the old one too). The issue isn't an infinite number of solutions (there are always an infinite number), it is whether there are multiple independent solution vectors (i.e. the dimension of the solution space is greater than one). So the error messages should probably be updated to reflect this.

[isaacsas]

Modulo that comment this is fine with me.

[TorkelE]

That make sense, I will update with new error/warning message (new and old ones)

[TorkelE]

New messages:

waring:
"The space of possible balanced versions of the reaction ($reaction) is greater than 1. This prevents the selection of a single appropriate balanced reaction. Instead, a basis for balanced reactions is returned. Note that we do not check if they preserve the set of substrates and products from the original reaction."

error (for system-level balancing)
"The space of possible balanced versions of the reaction ($reaction) is greater than 1. This prevents the selection of a single appropriate balanced reaction. No method to, in this case, automatically generate a valid reaction is currently implemented in balance_system.""

[isaacsas]

If tests pass happy for you to merge this.