fix!: handle sql/driver.Valuer types properly in slogjson

[ethanndickson]

Currently, if a field like sql.NullInt32 has Valid: False, sloghuman will export it's value as <nil>, regardless of it's String.
This is because it checks (driver.Valuer).Value().

However, slogjson currently sets the value to the json string of the raw struct:

{
  "fields": {
      "Code": "{Int32:0 Valid:false}",
      "ValidCode": "{Int32:12 Valid:true}"
  }
}

This PR handles this case by first checking if the type implements sql/driver.Valuer. If Valid is false then a JSON null value is produced:

{
  "fields": {
      "Code": null,
      "ValidCode": 12
  }
}

This matches the behaviour of sloghuman.

This is technically a breaking change, as these types are now T | null instead of String, where T is the corresponding JSON type of sql.Null<V>

[ethanndickson]

• fix!: handle sql/driver.Valuer types properly in slogjson #219 👈 (View in Graphite)
• main

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[coveralls]

Pull Request Test Coverage Report for Build bba9d76dbd5596a5a6dde53f28ff7ec985d4b3fa-PR-219

Details

• 4 of 6 (66.67%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 96.822%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
map.go	4	6	66.67%

Totals
Change from base Build 0ec81e6e67bb1fe88d4d068a6c7325f449008201:	-0.2%
Covered Lines:	792
Relevant Lines:	818

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💛 - Coveralls