feat(exercises): add JSR-354 workshop exercises (part1–part3)

Introduce hands-on exercises with tests covering:

* part1: MoneyExercises, ArithmeticExercises, RoundingExercises,
  FormattingExercises, ParsingExercises, IntegrationExercises
* part2: CurrencyConversionExercises, MonetaryOperatorExercises,
  MonetaryQueryExercises, MonetaryContextExercises,
  RoundingStrategyExercises
* part3: OrderExercises (end-to-end order workflow)

Use incomplete production methods with TODOs and complete JUnit 5 tests
(AssertJ only). Tests focus on observable behavior and avoid fragile
assertions (e.g., no fixed FX rates). Ensure clear progression from
basics to advanced concepts and final integration task.

.gitignore

@@ -0,0 +1,43 @@
+/target/
+/.gradle
+/build/
+!**/src/main/**/target/
+!**/src/test/**/target/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+# The following files are often generated by operating systems or desktop environments
+.DS_Store
+Thumbs.db
+
+# Eclipse and STS
+/.apt_generated
+/.classpath
+/.factorypath
+/.project
+/.settings
+/.springBeans
+/.sts4-cache
+
+# IntelliJ IDEA
+/.idea
+/*.iws
+/*.iml
+/*.ipr
+/out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+# NetBeans
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+nb-configuration.xml
+
+# VS Code
+/.vscode/
+
+# Moneta Exchange Rate Provider Cache
+/.resourceCache/