Improve filtering of generated code in the coverage reports

[alexander-yevsyukov]

This PR brings the changes to buildSrc recently adopted in Validation for filtering of proto-generated code from test coverage reports.

Other notable changes

• Agents instructions were included to avoid escaping backticks in version bump commit message.

[Copilot]

Pull request overview

This PR updates the JaCoCo coverage filtering logic in buildSrc to better exclude proto-/generated sources from coverage reports, including Kotlin sources generated by protoc-gen-kotlin.

Changes:

• Extend coverage filtering to consider Kotlin source roots and Kotlin-generated class naming (.kt, .proto.kt, synthetic *Kt classes).
• Simplify generated-class discovery by deriving class FQNs from source-relative paths (File.classNamesIn), and apply those when excluding compiled outputs.
• Add focused unit tests for the new source-file-to-class-name mapping logic; update agent skill docs for version bump commit subjects.

Reviewed changes

Copilot reviewed 2 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
buildSrc/src/test/kotlin/io/spine/gradle/report/coverage/FileExtensionsTest.kt	Adds tests for deriving JVM class FQNs from .java, .kt, and .proto.kt sources.
buildSrc/src/main/kotlin/io/spine/gradle/report/coverage/PathMarker.kt	Removes Java-specific path markers and renames output marker to MAIN_OUTPUT_FOLDER.
buildSrc/src/main/kotlin/io/spine/gradle/report/coverage/JacocoConfig.kt	Collects both Java and Kotlin main source directories for filtering/source reporting.
buildSrc/src/main/kotlin/io/spine/gradle/report/coverage/FileExtensions.kt	Introduces classNamesIn, updates compiled-class parsing marker, and adjusts docs/constants.
buildSrc/src/main/kotlin/io/spine/gradle/report/coverage/FileExtension.kt	Adds KOTLIN_SOURCE file extension.
buildSrc/src/main/kotlin/io/spine/gradle/report/coverage/CodebaseFilter.kt	Switches generated class name discovery to the new classNamesIn approach.
buildSrc/src/main/kotlin/io/spine/dependency/local/CoreJvmCompiler.kt	Bumps Core JVM Compiler snapshot version constants.
.agents/skills/bump-version/SKILL.md	Clarifies commit-subject backtick handling and adds a shell-safe example.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 8 changed files in this pull request and generated no new comments.