Add unit tests

[f1ammable]

• Also added commands to interpreter
• Tests include code coverage, linting and formatting

[github-actions]

Code Coverage Report

### Per-File Coverage Summary
Filename                      Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover    Branches   Missed Branches     Cover
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
callable.hpp                        1                 0   100.00%           1                 0   100.00%           1                 0   100.00%           0                 0         -
environment.cpp                    18                 0   100.00%           4                 0   100.00%          39                 0   100.00%          10                 0   100.00%
environment.hpp                     2                 0   100.00%           1                 0   100.00%           4                 0   100.00%           0                 0         -
error.cpp                           4                 0   100.00%           4                 0   100.00%          13                 0   100.00%           0                 0         -
error.hpp                           8                 0   100.00%           2                 0   100.00%          21                 0   100.00%           0                 0         -
expr.hpp                           38                15    60.53%          25                12    52.00%          64                37    42.19%           2                 2     0.00%
formatter.hpp                      58                 3    94.83%           9                 3    66.67%          99                 9    90.91%           2                 0   100.00%
interpreter.cpp                    43                 2    95.35%          18                 0   100.00%         135                 5    96.30%          36                 3    91.67%
object.hpp                         25                 1    96.00%          17                 1    94.12%         118                 2    98.31%           2                 0   100.00%
parser.cpp                        100                 2    98.00%          21                 0   100.00%         143                 0   100.00%          60                 8    86.67%
parser.hpp                         19                 0   100.00%           1                 0   100.00%           3                 0   100.00%          16                 0   100.00%
scanner.cpp                        80                 0   100.00%          12                 0   100.00%         120                 0   100.00%          68                 2    97.06%
scanner.hpp                         1                 0   100.00%           1                 0   100.00%           4                 0   100.00%           0                 0         -
stdlib.hpp                          9                 7    22.22%           6                 4    33.33%          18                14    22.22%           2                 2     0.00%
stmnt.hpp                          13                 1    92.31%           8                 1    87.50%          14                 1    92.86%           0                 0         -
token.hpp                           4                 0   100.00%           1                 0   100.00%           3                 0   100.00%           0                 0         -
util.cpp                           26                16    38.46%           3                 2    33.33%          39                24    38.46%          24                20    16.67%
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                             449                47    89.53%         134                23    82.84%         838                92    89.02%         222                37    83.33%

Detailed HTML report available in artifacts.

[f1ammable]

10/10 dev experience with gh actions