Added .__eq__ and .__hash__ to BaseMesh

[wyatt-fluidnumerics]

Description

After converting different mesh types to be classes in #2739 the hashing method used for identifying equal meshes breaks. The fix is to add .eq and .hash methods to the BaseMesh class.

Checklist

• Closes Unexpected warning about different meshes when combining models #2775
• This PR targets the correct branch (main for normal development, v3-support for v3 support)

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.
  • Describe how you used it (e.g., by pasting your prompt): I used claude code in plan mode to get information about how python's hash function hashes tuples. All code was written by myself.