feat: The Lurk evaluation in Loam

[winston-h-zhang]

This PR implements an initial version of the signal synthesis stage in the Loam compiler. We go from Loam to a fully synthesized program, and implement a minimal Lurk in the Loam syntax.

Notes:

• evaluation.lisp contains the Lurk implementation, as well as a suite of tests checking for correctness.
• Env representation was simplified back to conses for ease of initial implementation.
• Some changes for more ergonomic trace messages, builtin handling.
• Loam syntax a bit messy but cleanup left for later PR.

[winston-h-zhang]

@porcuquine To generally address your comments about env: I've simplified the current implementation to use cons based envs, mirroring the implementation in Rust Loam. So any matching on the :env tag won't be run anymore and some things have been commented out temporarily.