Use bazel module scala instead of workspace (#26)

Author: michalbogacz

BUILD.bazel

@@ -1,10 +1,17 @@
-load("@io_bazel_rules_scala//scala:scala.bzl", "setup_scala_toolchain")
+load("@rules_scala//scala:scala_toolchain.bzl", "scala_toolchain")
 
-setup_scala_toolchain(
-    name = "custom_scala_toolchain",
+scala_toolchain(
+    name = "custom_scala_toolchain_impl",
     scalacopts = [
         "-Wunused:all",
     ],
     strict_deps_mode = "error",
     unused_dependency_checker_mode = "warn",
 )
+
+toolchain(
+    name = "custom_scala_toolchain",
+    toolchain = ":custom_scala_toolchain_impl",
+    toolchain_type = "@rules_scala//scala:toolchain_type",
+    visibility = ["//visibility:public"],
+)

MODULE.bazel

@@ -1,4 +1,26 @@
 bazel_dep(name = "bazel_skylib", version = "1.7.1")
+bazel_dep(name = "rules_scala", version = "7.0.0")
+
+register_toolchains("//:custom_scala_toolchain")
+
+scala_version = "3.3.6"
+
+scala_config = use_extension(
+    "@rules_scala//scala/extensions:config.bzl",
+    "scala_config",
+)
+scala_config.settings(scala_version = scala_version)
+
+scala_deps = use_extension(
+    "@rules_scala//scala/extensions:deps.bzl",
+    "scala_deps",
+)
+scala_deps.settings(
+    fetch_sources = True,
+)
+scala_deps.scala()
+scala_deps.scalatest()
+
 bazel_dep(name = "rules_jvm_external", version = "6.7")
 
 maven = use_extension("@rules_jvm_external//:extensions.bzl", "maven")