feat: DSL parser rewrite (#25)

## Problem
The previous parser was imperative, had poorly defined syntax, was
missing the entire physical side, and was not maintainable (essentially
a hackathon-like POC). This PR solves all of these problems by designing
a better language and using a declarative parser.

## Summary of changes
- Better, more simplistic AST
- Support for ADTs
- Parsing with error recovery and useful messages
- Support map literals
- Much, much more expressive syntax to model query optimization (see
test cases for now, will release a formal specification eventually)

Author: AlSchlo

Cargo.lock

@@ -1,16 +1,13 @@
 [workspace]
-members = ["optd-core", "optd-datafusion", "optd-datafusion-cli"]
+members = ["optd-core", "optd-dsl", "optd-datafusion", "optd-datafusion-cli"]
 resolver = "2"
 
-
 [workspace.package]
 version = "0.1.0"
 edition = "2021"
 rust-version = "1.81.0"
 repository = "https://github.com/cmu-db/optd"
 
-
-
 [workspace.dependencies]
 anyhow = "1.0"
 trait-variant = "0.1.2"