Enhancement: Include metadata in BasicSymbolic isequal comparison

[bowenszhu]

• Fix isequal for BasicSymbolic should consider metadata #665

This pull request enhances the isequal function for BasicSymbolic to incorporate metadata in the comparison. Previously, metadata was ignored when checking for equality between two symbolic objects. This could lead to incorrect results when mathematically equivalent sysmbolic objects have different metadata, especially for #658.

This change ensures that two BasicSymbolic objects are considered equal only if they have the same expression type, the same symtypes, and identical metadata. This PR specifically supports the work done in #658 for internally handling hash collision.

[bowenszhu]

Following up on @AayushSabharwal's point from the Oct 31 meeting: including metadata in BasicSymbolic isequal is breaking ModelingToolkit integration tests. Should we prioritize metadata compatibility or maintaining the current integration tests? Need a decision here to move forward.

[AayushSabharwal]

Adding metadata equality to isequal would be breaking for SU and require a massive change to MTK to support. In the October 31st meeting, I was suggesting considering metadata specifically for hashconsing. Similar to the hash2 function, an isequal2 could be used to check for hash collisions. Effectively, something like:

h = hash2(sym)
cached = get(wvd, h, nothing)
if cached === nothing
    wvd[h] = sym
elseif isequal2(cached, sym)
    return cached
else
    return sym
end