Add unchecked return scanner plugin

[telemarkdigital-publisher]

Fixes #16. Adds an @veridion/plugin-unchecked-return workspace package that detects unchecked Solidity call, send, and delegatecall return values, including ignored calls and assigned-but-unvalidated success flags. Also adds focused tests and lets PluginRegistry accept initial plugins through its constructor for straightforward registration. Verification: corepack pnpm@9.1.0 --filter @veridion/plugin-unchecked-return test; corepack pnpm@9.1.0 --filter @veridion/plugin-unchecked-return typecheck; corepack pnpm@9.1.0 --filter @veridion/plugin-unchecked-return lint; corepack pnpm@9.1.0 --filter @veridion/plugin-unchecked-return build; corepack pnpm@9.1.0 --filter @veridion/scanner-core test; corepack pnpm@9.1.0 --filter @veridion/scanner-core typecheck; corepack pnpm@9.1.0 --filter @veridion/scanner-core lint; corepack pnpm@9.1.0 --filter @veridion/scanner-core build.

[telemarkdigital-publisher]

Pushed a formatter-only update in d00d60a after the PR lint workflow reported Prettier issues in plugins/unchecked-return/src/index.ts.

Local verification now passes for the changed plugin:

• prettier --check plugins/unchecked-return/src/index.ts
• tsc --noEmit
• eslint src --max-warnings 0
• vitest run src/index.test.ts (12 tests)

The refreshed CI run is currently action_required with no jobs, so it may need repository workflow approval before GitHub can rerun it.