Restructure main to have single update function

[charleskawczynski]

This PR restructures main.jl so that there is a single update function. This means that

        TC.zero_tendencies(self.GMV)
        Cases.update_surface(self.Case, self.GMV, self.TS)
        Cases.update_forcing(self.Case, self.GMV, self.TS)
        Cases.update_radiation(self.Case, self.GMV, self.TS)

        TC.update(self.GMV, self.TS)
        TC.update_GMV_diagnostics(self.Turb, self.GMV)

moves inside TC.update. This way, we can decompose TC.update into

• Update aux (compute diagnostic and non-local quantities)
• Compute RHS (compute tendencies, not new)
• Solve eqs (values = values + Δt*tendencies + implicit solves)

[charleskawczynski]

Results look fine

[charleskawczynski]

bors r+

[bors]

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