Fix basedpyright errors, remove plotting code, update gitignore

- Add pyright ignore comments for sympy typing issues in recurrence.py
  and recurrence_qbx.py (sum() return type, .subs() return type,
  ObjectArray1D vs ndarray)
- Broaden parameter types from sp.Expr to sp.Basic where .subs() results
  are passed
- Remove personal plotting code from test files
- Remove tracked experimental files (pgf, png, svg, ipynb)
- Update .gitignore to exclude *.ipynb, *.pgf, output.png, qbxrecurrence.svg

Author: hirish99

.gitignore

@@ -22,6 +22,9 @@ sumpy/_git_rev.py
 .asv
 
 *.vts
+*.ipynb
+*.pgf
+output.png
+qbxrecurrence.svg
 test/hirish_plotting
-test/test_eigenvalues.ipynb
 .vscode/settings.json