Restore marketplace licensing and add plugin smoke tests

[Dawsson]

Summary

• restore MCLicense marketplace key bootstrap for BuiltByBit and Polymart downloads
• add MockBukkit lifecycle and command coverage
• add a disposable real-Paper smoke test that installs ViaVersion through the public API
• run unit and Paper smoke tests on pull requests with read-only permissions and pinned actions

Verification

• ./gradlew test
• ./gradlew :plugin:paperSmoke

Actions security

• uses pull_request, not pull_request_target
• grants only read-only repository contents permission
• does not expose secrets
• disables checkout credential persistence
• pins actions to commit SHAs
• repository now requires approval for workflow runs from all external contributors

[Zoriot]

Seems to fix the active regression which was with the code currently at master.
Only tested in game, have not reviewed the code itself.

One issue which could be fixed here is that on a 1.21.11 Server it still suggests to update mclo.gs to 3.3.3 which is only combatible with mc 26.2 & 26.1 - https://modrinth.com/plugin/mclogs/version/3.3.3