Add z3regex Python module to translate Python regex syntax into Z3 regular expressions (#10095)

This PR adds a first-class Python API helper for expressing regex
constraints in familiar Python regex syntax and translating them into Z3
regex terms. The translator is implemented as a separate module
(`z3regex.py`) as requested, keeping regex conversion logic isolated
from core API files.

- **New Python regex translator module**
  - Adds `src/api/python/z3/z3regex.py`.
- Introduces `regex_to_re(pattern, flags=0, ctx=None)` to convert parsed
Python regex constructs into Z3 regex expressions.
- Supports core regular constructs (literals, classes/ranges,
alternation, grouping, quantifiers, categories, wildcard).
- Raises `NotImplementedError` for unsupported non-regular constructs
(e.g., features outside regular languages).

- **API/package integration**
  - Exposes the module via `src/api/python/z3/__init__.py`.
- Includes `z3/z3regex.py` in Python binding file copy/install flow in
`src/api/python/CMakeLists.txt`.

- **Doctest entrypoint support**
- Extends `src/api/python/z3test.py` with `z3regex` mode so translator
doctests can be run consistently with existing Python API doctest flows.

```python
from z3 import *
from z3.z3regex import regex_to_re

x = String("x")
r = regex_to_re(r"(ab|cd)+\d{2}")

s = Solver()
s.add(InRe(x, r))
```

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

src/api/python/CMakeLists.txt

@@ -9,6 +9,7 @@ set(z3py_files
   z3/z3num.py
   z3/z3poly.py
   z3/z3printer.py
+  z3/z3regex.py
   z3/z3rcf.py
   z3test.py
   z3/z3types.py