* Add `EvaluatorOptions.externalModuleReaders` and `EvaluatorOptions.externalResourceReaders`.
* Add `ExternalReaderClient` to host the child process side of the external reader workflow.
* Add Pkl 0.26 features
* Add multi-version support
* Bump Pkl version in CI
* Update CI
* Split tests across different Pkl versions
Co-authored-by: Daniel Chao <daniel.h.chao@gmail.com>