Fix for Exec(...) mocking with non-standard SQL data types ([]string)

[berupp]

Trying to address this issue.

I added two tests in the first change set:

• TestCustomValueConverterQueryScan is mocking Query/Scan using a custom driver.ValueConverter as described here
• TestCustomValueConverterExec is attempting to mock an insert using Exec

TestCustomValueConverterExec fails due to driver.IsValue(darg)-check, which basically filters all non-default types.
I think it is safe to remove this check, and the following reflect.DeepEquals() will successfully handle List and Map data types that are more common these days.

[codecov-io]

Codecov Report

Merging #195 into master will increase coverage by 0.24%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
+ Coverage   90.87%   91.11%   +0.24%     
==========================================
  Files          15       15              
  Lines         745      743       -2     
==========================================
  Hits          677      677              
+ Misses         49       48       -1     
+ Partials       19       18       -1

Impacted Files	Coverage Δ
expectations_go18.go	86.66% <ø> (+5.41%)	⬆️

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[berupp]

Note: I changed the Exec(...) fix to be supported by 1.9+ due to driver.NamedValueChecker support being introduced in 1.9 and that seems required for the registered custom driver.ValueConverter to work

[l3pp4rd]

thanks, good work