Fix memory leaks

[kiedtl]

Currently, basically no memory is ever freed. The allocator isn't even deinit'd.

Start out by writing routines for recursively freeing ASTNode's, then start deinit'ing the GPA, and piping the output traces through less to find out what else is not being deallocated.

[kiedtl]

• SmolStr/CompactString implementation in Zig
• Analysis with Heaptrack

[kiedtl]

Worked a bit on this. From analysing allocator deinit stderr output, unfreed allocations are down from 12752 unfreed allocations (before work began), to 6178 unfreed allocations, to 418.

Most of the remaining unfreed allocations seems to be coming from TypeInfo's and random lexer/AST nodes that seem to have been orphaned(?).

Note to future self: create a Box type of the form

pub fn Box(comptime T: type) type {
    return struct {
        const Inner = struct {
            allocation: T,
            freed: bool = false,
        }
        inner: *Inner,
    };
}

that tracks whether an allocation has been freed or not. Then, use it in TypeInfo for Fn, AnySet, Of, Expr.Fn, etc.