DEP: remove _is_number(Expr) from expr.pyi file

[Zeroto521]

_is_number(Expr) always return False. Because Expr doesn't have __float__ method and it isn't a number type.

In [1]: from pyscipopt import Model, Expr

In [2]: from pyscipopt.scip import CONST

In [3]: e = Expr({CONST: -1.0})

In [4]: float(e)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[4], line 1
----> 1 float(e)

TypeError: float() argument must be a string or a real number, not 'pyscipopt.scip.Expr'

In [5]: float(e+1)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[5], line 1
----> 1 float(e+1)

TypeError: float() argument must be a string or a real number, not 'pyscipopt.scip.Expr'

[Copilot]

Pull request overview

This PR removes dead code from the Expr class by eliminating checks for _is_number(self) which always return False since Expr instances cannot be converted to float.

Changes:

• Removed unreachable code branches in __add__, __mul__, and __rtruediv__ methods that checked if self is a number
• Simplified __rtruediv__ implementation by removing the always-false conditional check

---

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[Zeroto521]

This pr is ready.
CI fails due to performance jitter. Especially, the traceline mark is set to True.

=========================== short test summary info ============================
FAILED tests/test_matrix_variable.py::test_matrix_dot_performance[50] - assert False
 +  where False = isGT(2.9845094680786133, 3.222688674926758)
 +    where isGT = <pyscipopt.scip.Model object at 0x7f039845b440>.isGT
FAILED tests/test_matrix_variable.py::test_matrix_dot_performance[100] - assert False
 +  where False = isGT(25.479017972946167, 25.84245491027832)
 +    where isGT = <pyscipopt.scip.Model object at 0x7f0364f4b5c0>.isGT
= 2 failed, 408 passed, 104 skipped, 11 xfailed, 4 warnings in 157.89s (0:02:37) =
/opt/hostedtoolcache/Python/3.11.14/x64/lib/python3.11/site-packages/coverage/control.py:958: CoverageWarning: No data was collected. (no-data-collected); see https://coverage.readthedocs.io/en/7.13.1/messages.html#warning-no-data-collected
  self._warn("No data was collected.", slug="no-data-collected")