Rename `ObjectSourceExtension` now that it serves both `@ObjectSource` and `@TableSource`

[em3s]

Background

ObjectSourceExtension now dispatches for both @ObjectSource and @TableSource (after #273). The name no longer reflects what the class does.

Bundling the rename into #273 would have dropped the combined similarity below git's 50% rename-detection threshold, causing git blame to lose original authorship after a squash merge. A standalone rename PR keeps similarity at ~96% and preserves blame.

Task

• Rename ObjectSourceExtension.kt to a neutral name (e.g. SourceExtension.kt)
• Update the class declaration to match
• Update @ExtendWith(ObjectSourceExtension::class) in ObjectSourceParameterizedTest.kt
• (Optional) Also rename ObjectSourceInvocationContext / ObjectSourceParameterResolver — both now serve both annotations

Done When

• File and class are renamed, references updated
• ./gradlew :core:test green

[em3s]

@zipdoki could you take this one? 🙏

[zipdoki]

@em3s
I'd like to take this one! I'll work on a fix and open a PR soon.