Drops`dev.mokksy:mokksy` dependency
## Motivation and Context
`mokksy` is a niche, single-maintainer library with very limited
external adoption, introduced by its own author. Keeping a test-only
dependency on it is unnecessary supply-chain exposure given that the two
patterns already used in this repo, `MockEngine` for transport-level
tests and `embeddedServer` for integration-level tests, cover everything
it provided.
## Breaking Changes
none
## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed
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