Add Scalafix Plugin and Configuration for RemoveUnused

[khajavi]

No description provided.

[Copilot]

Pull request overview

Adds Scalafix tooling to the build and enables the RemoveUnused rule, including SemanticDB configuration required for semantic rules.

Changes:

• Add sbt-scalafix plugin to the sbt build.
• Enable SemanticDB generation in the build to support Scalafix rules.
• Add a root .scalafix.conf enabling RemoveUnused.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
project/plugins.sbt	Adds the sbt-scalafix sbt plugin dependency.
build.sbt	Enables SemanticDB (required for semantic Scalafix rules).
.scalafix.conf	Configures Scalafix to run the RemoveUnused rule.