Support Python 3.15

[ikrommyd]

Closes #920

Describe your changes
We switch to enum class instead of enum because cython uses IntFlag for enum and that messes up negative values in 3.15.
We also remove the ".llvm." in symbol check in hybrid_stack_trace as that no longer appears to be the case.
We add 3.15 in CI and we have to use the cibuildwheel release candidate to get 3.15.

Testing performed
Tested locally with 3.14 and 3.15 and the tests pass. We'll see what the CI says

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.34%. Comparing base (4a99614) to head (95bdbb4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #927      +/-   ##
==========================================
- Coverage   92.43%   92.34%   -0.09%     
==========================================
  Files          99       99              
  Lines       11785    11785              
  Branches      429      429              
==========================================
- Hits        10893    10883      -10     
- Misses        892      902      +10     

Flag	Coverage Δ
cpp	92.34% <ø> (-0.09%)	⬇️
python_and_cython	92.34% <ø> (-0.09%)	⬇️

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[da-woods]

I do intend to fix the negative enum issue in Cython before 3.15 - I just haven't decided exactly how (or done it) yet.

The other thing you could do rather than changing the numbers is change the enum to cpdef enum class. This creates a c++ enum class instead (which is probably fine here) and creates an IntEnum rather than an IntFlag which should avoid the issue.

[ikrommyd]

@da-woods I tried switching to enum class and tests are fine locally. We'll see what CI says.

[ikrommyd]

Rebased to main. Had to fix conflicts in workflows.