feat: Port async sourcetransformer to Rust

[BulkBeing]

Attempt to migrate (to Rust FFI version) one component at a time from pure python pynumaflow package itself, without the need for a separate pynumaflow_lite package.

[vigith]

are you sure we want to do this now? there are some breaking changes, esp. around streaming interface. let's make sure pynumaflow-lite is complete and is adopted before we switch.

[yhl25]

Can we make pynumaflow-lite backward compatible before porting the pynumaflow to use ffi?

[vigith]

Can we make pynumaflow-lite backward compatible before porting the pynumaflow to use ffi?

it is more about cleanup and standardization.

[BulkBeing]

Will keep pynumaflow-lite as separate package itself. I will work on implementing the CI pipeline and publishing that package.