refactor: Refactor and simplify, removing legacy lurk (#945)

* refactor: Refactor store module and remove let_store tests

- Changed the `store` module's visibility to private, restricting its direct accessibility.
- Eliminated the `let_store` macro, enforcing all `Store` manipulations to be conducted without it.
- Removed the `lurk_macro_test.rs` file, which contained major test functions, causing significant changes to the test suite.

* refactor: Refactor and simplify, removing legacy lurk

Cleans up Lurk Alpha structures.

In detail:
- Entire deletion of files `src/expr.rs`, `src/writer.rs`, `src/cont.rs` and `src/ptr.rs`, which held sizeable and complex code structures and functionalities.
- Significant simplification and removal of code in `src/circuit/gadgets/data.rs` and `src/circuit/gadgets/pointer.rs`, affecting allocation and handling of various tags, symbols, pointers, and numbers.
- Removal of implementations relating to `Store<F>`, `GlobalAllocations` and `TypePredicates` among others, shifting away from Lurk Alpha.
- Substantial rewrite in `lib.rs`, removing outdated modules and adding new ones. A tiny new `store` module is added with an `Error` struct.
- Changes to `ZExpr` and `ZStore` handling in `z_expr.rs` and `z_store.rs` respectively.
- Deletion of substantial functions and units tests related to `CaseConstraint` and `multi_case` in `src/circuit/gadgets/case.rs`.
- Removal of code related to `ptr` and `cont` handling across multiple files.
- Major codebase cleanup through removal of unused imports, functions, structs, modules and files across multiple directories.

lurk-macros/src/lib.rs

@@ -291,15 +291,6 @@ impl Lurk {
     }
 }
 
-#[proc_macro]
-/// Binds a mutable `Store` to the variable `s_`, which is (somewhat unfortunately) hard-coded into the `lurk!` macro.
-/// Users should therefore avoid using `s_` for other purposes, and will need to use `s_` directly when manipulating the
-/// `Store`. The name `s_` was chosen to walk the line between obscurity and brevity/clarity. Accidental collisions are
-/// undesirable, but so is an awkward or unwieldy name.
-pub fn let_store(_tokens: TokenStream) -> TokenStream {
-    quote!(let s_ = &mut Store::<Fr>::default();).into()
-}
-
 #[proc_macro]
 pub fn lurk(tokens: TokenStream) -> TokenStream {
     Lurk::parse_raw(tokens.into()).emit()