feat(stdlib): add re (regular expressions) module bindings (#273)

* feat(stdlib): add re (regular expressions) module bindings

Adds F# bindings for Python's re module, covering:

- Match object: group(), groups(), groupdict(), start(), end(), span(),
  expand(), string, pos, endpos, lastindex, lastgroup
- Pattern object: match(), search(), fullmatch(), findall(), finditer(),
  sub(), subn(), split(), pattern, flags, groups, groupindex
- Module-level functions: compile, match, search, fullmatch, findall,
  finditer, sub, subn, split, escape, purge
- Flags module: IGNORECASE/I, MULTILINE/M, DOTALL/S, ASCII/A,
  LOCALE/L, UNICODE/U, VERBOSE/X, NOFLAG

Also adds 42 tests in test/TestRegex.fs covering all key APIs.

Note: CHANGELOG.md is intentionally not updated per repository policy.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* refactor(stdlib): drop redundant Emit attrs in Regex bindings

Strip [<Emit>] attributes that simply reproduce the default Fable
codegen (positional-only IExports overloads with flags, string-key
Match accessors, no-arg `end()`). Per BINDINGS_GUIDE.md and the
Random.fs convention, [<Emit>] should only appear when it changes
generated output (int casts, keyword args, list wraps).

Also collapse the duplicate-literal short flag aliases
([<Literal>] let I = 2) into literal aliases of the long names
([<Literal>] let I = IGNORECASE) so the integer values live in
one place.

Generated Python is byte-identical for the affected sites; all
430 tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Dag Brattli <dag@brattli.net>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 4 people

src/Fable.Python.fsproj

@@ -28,6 +28,7 @@
     <Compile Include="stdlib/Itertools.fs" />
     <Compile Include="stdlib/Datetime.fs" />
     <Compile Include="stdlib/Functools.fs" />
+    <Compile Include="stdlib/Regex.fs" />
     <Compile Include="stdlib/Queue.fs" />
     <Compile Include="stdlib/String.fs" />
     <Compile Include="stdlib/Sys.fs" />