feat: halstead complexity printer

[devtooligan]

• this pr adds a new printer which calculates and displays the Halstead complexity metrics

Halstead complexity core metrics:
+-----------------------+-----------------+------------------+----------------+-----------------+
|        Contract       | Total Operators | Unique Operators | Total Operands | Unique Operands |
+-----------------------+-----------------+------------------+----------------+-----------------+
| SimpleVulnerableToken |        74       |        11        |      138       |        44       |
+-----------------------+-----------------+------------------+----------------+-----------------+

Halstead complexity extended metrics1:
+-----------------------+------------+----------------+------------------+--------+
|        Contract       | Vocabulary | Program Length | Estimated Length | Volume |
+-----------------------+------------+----------------+------------------+--------+
| SimpleVulnerableToken |     55     |      212       |       278        |  1226  |
+-----------------------+------------+----------------+------------------+--------+

Halstead complexity extended metrics2:
+-----------------------+------------+--------+------+----------------+
|        Contract       | Difficulty | Effort | Time | Estimated Bugs |
+-----------------------+------------+--------+------+----------------+
| SimpleVulnerableToken |     17     | 21142  | 1175 |     0.255      |
+-----------------------+------------+--------+------+----------------+

INFO:Slither:./examples/printers/human_printer.sol analyzed (1 contracts)

[montyly]

I think we should apply the same changes I did for #1882 (comment) / e855728

If no one can take the lead on it, I will do it before tomorrow

[devtooligan]

@montyly I think that's a great suggestion I can take care of this next week.