Improve console output, reject (required) Empty

[alexander-yevsyukov]

This PR:

1. Improves the console output of warnings on using unsigned types (Align warning message in console for better readability #220).
2. Produce compile-time errors when Empty message is claimed as (required), including in repeated and map values (Produce compile-time error on (required) set on an Empty field #146).
3. Adds tests for (set_once) constraint (Implement negative tests for (set_once) and (goes) #175).

[Copilot]

Pull request overview

This PR tightens validation option semantics and improves developer feedback by introducing compile-time rejection for invalid (required) usage on google.protobuf.Empty, expanding (set_once) test coverage to external message types, and enhancing compiler warning readability. It also adds an api-discovery helper (scripts + skill docs) aimed at avoiding repeated Gradle-cache JAR unzips, along with routine version/docs updates.

Changes:

• Reject (required) on google.protobuf.Empty (including repeated and map<_, Empty>) at compile time, with dedicated compilation-error fixtures/tests.
• Add integration coverage for (set_once) on an external dependency type (google.protobuf.Timestamp) via new proto fixture + tests.
• Improve console output for unsigned-integer warnings and introduce api-discovery scripts/skill documentation; bump snapshot version and regenerate dependency reports.

Reviewed changes

Copilot reviewed 26 out of 26 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
version.gradle.kts	Bumps published library snapshot version.
docs/dependencies/pom.xml	Aligns docs artifact version with the new snapshot.
docs/dependencies/dependencies.md	Regenerates dependency/license report for the new version.
context/src/main/kotlin/io/spine/tools/validation/option/required/RequiredOption.kt	Adds compile-time rejection for (required) on google.protobuf.Empty (incl. list/map value cases).
context-tests/src/testFixtures/proto/spine/validation/required_option_spec.proto	Adds compilation-failure fixtures for (required) applied to Empty in different shapes.
context-tests/src/test/kotlin/io/spine/tools/validation/RequiredOptionSpec.kt	Adds compilation-error assertions for the new Empty rejection cases.
tests/validating/src/testFixtures/proto/spine/test/tools/validate/required.proto	Removes runtime fixture that previously demonstrated (required) + Empty behavior.
tests/validating/src/test/kotlin/io/spine/test/options/required/RequiredMessageITest.kt	Removes runtime test now superseded by compile-time rejection.
tests/validating/src/testFixtures/proto/spine/test/tools/validate/set_once_fields.proto	Adds Timestamp import and Measurement message for (set_once) external-type coverage.
tests/validating/src/testFixtures/kotlin/io/spine/test/options/setonce/SetOnceTestEnv.kt	Adds reusable Timestamp test constants.
tests/validating/src/test/kotlin/io/spine/test/options/setonce/SetOnceFieldsITest.kt	Adds integration tests ensuring (set_once) works for external message types.
java/src/main/kotlin/io/spine/tools/validation/java/generate/option/bound/BoundedFieldGenerator.kt	Refactors unsigned-integer warning message to multi-line for readability.
CLAUDE.md	Adds workflow guidance to use api-discovery when inspecting cached dependencies.
.agents/skills/api-discovery/SKILL.md	Documents the api-discovery workflow, bootstrap, and stale-sibling refresh procedure.
.agents/scripts/api-discovery/discover	Adds resolver script to map Maven coords to local sources (sibling-first, cache fallback).
.agents/scripts/api-discovery/extract-sources	Adds cached extraction of -sources.jar into a workstation cache.
.agents/scripts/api-discovery/update-sibling	Adds guarded git pull --ff-only helper for stale sibling repos (opt-in).
.agents/scripts/api-discovery/clean-cache	Adds manual cache pruning utility.
.agents/scripts/api-discovery/lib/common.sh	Shared helpers for parsing, resolution, and cache path logic.
.agents/scripts/api-discovery/README.md	Implementation/reference docs for the api-discovery scripts.
.agents/scripts/api-discovery/.gitignore	Ignores per-developer workspace-root override file.
.agents/tasks/reject-required-on-empty.md	Task log/planning doc for the compile-time (required) + Empty work.
.agents/tasks/issue-175-set-once-timestamp.md	Task log/planning doc for the (set_once) + Timestamp integration test.
.agents/tasks/api-discovery.md	Task log/planning doc for the api-discovery feature.
.agents/tasks/prohibit-automatic-commits.md	Task doc describing commit-safety policy work (process-only).

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Pull request overview

Copilot reviewed 27 out of 28 changed files in this pull request and generated 3 comments.

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