Stubless RPC PoC dynamic linker

[vigoo]

This is the first of the two proof-of-concept steps that re prerequisites for implementing the actual dynamic linker for stubless RPC.

For this ticket:

• choose the simplest RPC example from the tests created in Create a worker executor test suite for stubless RPC #1147
• add a dynamic linking step into worker executor (similarly how wRPC does)
• write code that works only for that specific use case - hardcoding the known input/output types, etc and implementing the necessary conversions from whatever the linker callback provides to what our RPC implementation requires
• make sure the RPC implementation (the whole durable context) is accessible in the linker callback
• test that the (hardcoded) dynamic RPC works