fix(SU2_CFD,SU2_PY,Common): Fix typos, code style, and safety guards

[shbhmexe]

Proposed Changes

This PR addresses code quality issues across the SU2 codebase:

Typo Fixes (Comment-only)

1. "approxiations" → "approximations" in 5 C++ solver files
2. "generilize" → "generalize" in CEulerSolver.cpp (4 occurrences)

Python Code Style (PEP8)

3. Replace type(x) == list with isinstance(x, list) in gradients.py and functions.py

C++ Safety Improvements

4. Add zero-distance guard in CHeatSolver.cpp (lines 640, 671)

   • Changed /dist to /fmax(dist, EPS) to prevent potential division by zero

5. Remove redundant 1.0* multiplication in CRadP1Solver.cpp (lines 323, 397)

C++ Bug Fixes (Common)

6. Fix float literal in CSysMatrix.cpp (line 160)

   • Changed (nPointDomain + 1.0) to (nPointDomain + 1) for GPU array allocation
   • Using float for array sizing is incorrect type usage

7. Remove redundant 1.0* in wall_model.cpp (line 374)

Related Work

No related issues. This is a cleanup PR to improve code quality and robustness.

PR Checklist

• I am submitting my contribution to the develop branch.
• My contribution generates no new compiler warnings.
• My contribution is commented and consistent with SU2 style.
• I used the pre-commit hook to prevent dirty commits.
• I have added a test case that demonstrates my contribution, if necessary.
• I have updated appropriate documentation, if necessary.

Impact

• Typo fixes: No functional changes (comment-only)
• Python style: Functionally equivalent, follows PEP8
• CHeatSolver.cpp: Adds safety for edge cases
• CSysMatrix.cpp: Fixes type correctness for GPU memory allocation
• CRadP1Solver.cpp & wall_model.cpp: Code cleanup