Multi-target gate circuit art improvement

[Morcifer]

This PR has a proposed fix for issue #2184, but it mainly includes refactoring of the circuit-art code based on comments from PR #2126.

The only real functionality change in this code is that multi-target gates get extra lines that behave in the same way as measurement lines, in order to better convey the qubits involved.

For example, a circuit like this one:

use q0 = Qubit();
use q1 = Qubit();
Rxx(1.0, q0, q1);

use q2 = Qubit();
use q3 = Qubit();
Rxx(1.0, q2, q3);

instead of rendering as

q_0    ─ rxx(1.0000) ─
q_1    ─ rxx(1.0000) ─
q_2    ─ rxx(1.0000) ─
q_3    ─ rxx(1.0000) ─

will instead render as

q_0    ─ rxx(1.0000) ─
              ┆
q_1    ─ rxx(1.0000) ─
q_2    ─ rxx(1.0000) ─
              ┆
q_3    ─ rxx(1.0000) ─

This is very similar to what we get if we measure the first qubit of each of these two-qubit gate, i.e.

q_0    ─ rxx(1.0000) ─── M ──
              ┆          ╘═══
q_1    ─ rxx(1.0000) ────────
q_2    ─ rxx(1.0000) ─── M ──
              ┆          ╘═══
q_3    ─ rxx(1.0000) ────────

On top of this change in rendering, the first few commits in this PR are actually just code refactoring. As such, it's probably best to review this PR commit by commit, for two reason - a. it's going to be much easier to follow, and b. any of these commits can be reverted if you think they make the code more complicated instead of making it easier to read.

The commits are as follows:

1. a400655 A rework of PR Long gate in ASCII art circuits - lengthen column width when necessary #2126, which, to be honest, is how I think I should have implemented it in the first place.
2. c141799 A cleanup based on this comment. It makes the code significantly better, in my opinion.
3. 4012ee8 A small simplification to have the ColumnRenderer have a new method which is in charge of making sure that the column width is an odd number, and also a Default trait implementation for the case where we don't need a specific width.
4. cfa7382 This is the actual enhancement - it makes sure there is a classical line (same as what you get from a measurement) if there are two consecutive qubits for the same operation. If you think there is a better solution to make the rendering clearer, let me know. But of the ones I could think of, I found this one to be the least disruptive one (to both the existing code, and the existing circuits).

[minestarks]

Thank you for the fix and additional test cases. Just a few requests for readability.

[minestarks]

Heads up to @ScottCarda-MS who I think has been working near this code.

[minestarks]

Thanks @Morcifer !