Add @DbUnitRowCountCheck annotation for the row count check feature

[jeffjensen]

Fronts the row count check feature delivered in #939 with a declarative annotation,
following the same class/method precedence as the rest of the #753 annotation family.

Ask

Add @DbUnitRowCountCheck, a class- and method-level annotation that enables or
disables the row count check (#939) and configures its exclude list, without
touching DatabaseConfig directly:

• enabled (default true when the annotation is present) turns the check on for
  the annotated scope, overriding whatever DatabaseConfig.FEATURE_ROW_COUNT_CHECK
  or the dbunit.rowCountCheck.enabled system property says.
• exclude sets the table-name exclude patterns for that scope, replacing (not
  merging with) any class-level exclude when declared at the method level - method
  overrides class the same way the rest of the Add dbUnit annotations for declarative test setup, verification, and configuration #753 family works.
• Method-level annotation overrides class-level; declaring neither leaves
  DatabaseConfig/system-property precedence untouched.

Wires into DbUnitExtension (JUnit 5/6): captures the row-count baseline in
beforeTestExecution(), verifies it in afterTestExecution(), and skips the verify
when the test itself already failed so the check never masks the real failure.

Notes

Depends on #939 (the row count check feature itself) and #753 (the annotation
vocabulary and execution model this plugs into).