feat: add support for NUMERIC type

[olavloite]

Adds support for the NUMERIC data type.

[codecov]

Codecov Report

Merging #185 into master will decrease coverage by 0.76%.
The diff coverage is 55.17%.

@@             Coverage Diff              @@
##             master     #185      +/-   ##
============================================
- Coverage     72.17%   71.40%   -0.77%     
- Complexity     1094     1104      +10     
============================================
  Files            24       24              
  Lines          3292     3396     +104     
  Branches        495      525      +30     
============================================
+ Hits           2376     2425      +49     
- Misses          723      756      +33     
- Partials        193      215      +22     

Impacted Files	Coverage Δ	Complexity Δ
...ud/spanner/jdbc/AbstractJdbcPreparedStatement.java	90.24% <0.00%> (-0.61%)	51.00 <0.00> (-1.00)
...ogle/cloud/spanner/jdbc/JdbcParameterMetaData.java	15.27% <0.00%> (ø)	5.00 <0.00> (ø)
...a/com/google/cloud/spanner/jdbc/JdbcResultSet.java	74.24% <0.00%> (-4.57%)	186.00 <0.00> (ø)
...ogle/cloud/spanner/jdbc/JdbcResultSetMetaData.java	78.68% <0.00%> (-7.76%)	41.00 <0.00> (ø)
...google/cloud/spanner/jdbc/AbstractJdbcWrapper.java	68.96% <30.76%> (-8.35%)	53.00 <2.00> (+2.00)	⬇️
.../google/cloud/spanner/jdbc/JdbcParameterStore.java	50.49% <45.45%> (+0.11%)	127.00 <0.00> (+1.00)
...va/com/google/cloud/spanner/jdbc/JdbcDataType.java	58.06% <50.00%> (-0.87%)	4.00 <0.00> (ø)
...m/google/cloud/spanner/jdbc/JdbcTypeConverter.java	72.19% <55.55%> (-1.61%)	99.00 <0.00> (+8.00)	⬇️
...oogle/cloud/spanner/jdbc/JdbcDatabaseMetaData.java	95.47% <100.00%> (+0.24%)	180.00 <0.00> (ø)
... and 1 more

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[skuruppu]

@olavloite the tests are now passing 🎉

If you could please take a look at the other failures, that would be awesome.

[olavloite]

@skuruppu Ah, cool. I'll look into the other failures and update the PR.