Added singleton Put for doobie enums

[felix-hedenstrom]

At $work we've have a lot of enums like

sealed trait FooStatus extends EnumEntry.UpperSnakecase

object FooStatus extends enumeratum.Enum[FooStatus] with DoobieEnum[FooStatus]:
  val values = findValues

  case object Initiated        extends FooStatus
  case object Completed        extends FooStatus

which are used in fragments with status = ${FooStatus.Initiated: FooStatus}. We must manually widen the type in order for the Write[FooStatus] instance to be found.

This PR makes Write-instances available for all singleton values in an enumeratum-doobie Enum. We can now write
status = ${FooStatus.Initiated} which is a lot cleaner.

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✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.76%. Comparing base (7948eb5) to head (2d77b48).
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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #467      +/-   ##
==========================================
+ Coverage   85.71%   85.76%   +0.05%     
==========================================
  Files          63       64       +1     
  Lines         511      513       +2     
  Branches       34       34              
==========================================
+ Hits          438      440       +2     
  Misses         73       73              

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[Copilot]

Pull request overview

This PR improves enumeratum-doobie ergonomics by making Doobie Write instances available for singleton enum entries (e.g., FooStatus.Initiated.type), removing the need to manually widen singleton values to the parent enum type when using them in SQL fragments.

Changes:

• Add an implicit singleton Put instance for DoobieEnum entries, enabling Write derivation for singleton values.
• Add an implicit singleton Put instance for DoobieValueEnum entries, enabling Write derivation for singleton values.
• Extend existing ScalaTest specs to assert Write[...] availability for representative singleton enum values.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
enumeratum-doobie/src/main/scala/enumeratum/DoobieEnum.scala	Adds enumSingletonPut to provide Put (and thus Write) for singleton enum entries.
enumeratum-doobie/src/main/scala/enumeratum/values/DoobieValueEnum.scala	Adds enumSingletonPut to provide Put (and thus Write) for singleton value-enum entries.
enumeratum-doobie/src/test/scala/enumeratum/DoobieEnumSpec.scala	Adds a test that Write can be summoned for a singleton enum entry type.
enumeratum-doobie/src/test/scala/enumeratum/values/DoobieValueEnumSpec.scala	Adds tests that Write can be summoned for singleton value-enum entry types (Int/Long/Short examples).

[lloydmeta]

LGTM. Will merge when I have time to release as well.

[lloydmeta]

Released in 1.9.7