Add gauge_equiv options

[kvid]

Avoid gauge equivalents bugs as reported in #282 by enabling the user to select the proper method for computing equivalents that fits the current wire harness.

1. The current implementation requires Python 3.10+. Either rewrite slightly to support older versions, or change the Wireviz required Python versions.

2. Find proper default values for the new options. Please test this branch and suggest default values that might be useful for most users.

Alternative 1:

options:
  gauge_equiv:
    show: false
    rounding: nearest
    mm2: 3
    awg: [40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, "00", "000", "0000"]
    match:
      poor: 10
      invalid: 50

3. Should probably rename Cable.show_equiv to Cable.gauge_equiv for consistency with the new options attribute and to improve code readability. In addition, it removes a conflict with a possible future length_equiv attribute.

4. Maybe consider also supporting kcmil?

[sbennett18]

Minor typo precentage --> percentage

[kvid]

Thank you for reviewing and catching my typo!

I didn't expect much attention about this PR while it still is a draft, so your message was a nice surprise. 😄