bpo-43553: Improve sqlite3 test coverage

[erlend-aasland]

llvm-cov report after this PR:

Filename                      Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
prepare_protocol.c                 20                17    15.00%           4                 3    25.00%          22                15    31.82%
util.c                             65                21    67.69%           3                 0   100.00%          80                26    67.50%
module.c                          313                52    83.39%          11                 1    90.91%         245                51    79.18%
row.c                             214                44    79.44%          13                 1    92.31%         158                19    87.97%
microprotocols.c                   79                 8    89.87%           3                 0   100.00%          98                15    84.69%
connection.c                     1250               163    86.96%          46                 0   100.00%        1332               175    86.86%
module.h                            1                 0   100.00%           1                 0   100.00%           3                 0   100.00%
cursor.c                          875               114    86.97%          23                 0   100.00%         835               124    85.15%
statement.c                       355                26    92.68%          11                 0   100.00%         421                36    91.45%
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                            3172               445    85.97%         115                 5    95.65%        3194               461    85.57%

For comparison; coverage before this PR:

Filename                      Regions    Missed Regions     Cover   Functions  Missed Functions  Executed       Lines      Missed Lines     Cover
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
prepare_protocol.c                 20                17    15.00%           4                 3    25.00%          22                15    31.82%
util.c                             65                21    67.69%           3                 0   100.00%          80                26    67.50%
module.c                          313                65    79.23%          11                 4    63.64%         245                66    73.06%
row.c                             214                45    78.97%          13                 1    92.31%         158                23    85.44%
microprotocols.c                   79                24    69.62%           3                 0   100.00%          98                31    68.37%
connection.c                     1250               209    83.28%          46                 1    97.83%        1332               224    83.18%
module.h                            1                 0   100.00%           1                 0   100.00%           3                 0   100.00%
cursor.c                          875               122    86.06%          23                 0   100.00%         835               127    84.79%
statement.c                       355                26    92.68%          11                 0   100.00%         421                36    91.45%
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TOTAL                            3172               529    83.32%         115                 9    92.17%        3194               548    82.84%

https://bugs.python.org/issue43553

[pablogsal]

Nice work!

[erlend-aasland]

Thanks, and thanks for reviewing! Having better coverage makes me feel better when I do all these sqlite3 experiments 😅