Implement `Circuit.append`

[rafaelha]

Implement tsim.Circuit.append as a light wrapper around stim.Circuit.append. This should be a light wrapper in the sense that self._stim_circ.append can be called.

The only thing that needs to be taken care of is turning "T", "R_X", "R_Y", "R_Z", "U3" instructions into the format Stim understands. For example:

        T 0 1           → S[T] 0 1
        T_DAG 0 1       → S_DAG[T] 0 1
        R_Z(0.3) 0      → I[R_Z(theta=0.3*pi)] 0
        R_X(0.25) 0     → I[R_X(theta=0.25*pi)] 0
        R_Y(-0.5) 0     → I[R_Y(theta=-0.5*pi)] 0
        U3(0.3, 0.24, 0.49) 0 → I[U3(theta=0.3*pi, phi=0.24*pi, lambda=0.49*pi)] 0

[jaideepkathiresan]

Hi @rafaelha, I believe I can fix this. Can you assign this issue to me?

[rafaelha]

Sounds good!