Add _test_simple_multiple_platforms_with_extras

Run with:
```console
bazel test //tests/pypi/extension:test_simple_multiple_platforms_with_extras
```

Author: hartikainen

tests/pypi/extension/extension_tests.bzl

@@ -407,6 +407,93 @@ new-package==0.0.1 --hash=sha256:deadb00f2
 
 _tests.append(_test_simple_multiple_python_versions)
 
+def _test_simple_multiple_platforms_with_extras(env):
+    """TODO(hartikainen): Test that reproduces a multi-platform-with-extras issue."""
+    # This test case is based on my issue where different requirement strings for the same package
+    # (`jax` vs `jax[cuda12]`) for multiple platforms caused a "duplicate library" error (for details,
+    # see https://github.com/bazel-contrib/rules_python/issues/2797#issuecomment-3143914644).
+    pypi = _parse_modules(
+        env,
+        module_ctx = _mock_mctx(
+            _mod(
+                name = "rules_python",
+                parse = [
+                    _parse(
+                        hub_name = "pypi",
+                        python_version = "3.12",
+                        download_only = True,
+                        requirements_by_platform = {
+                            "requirements.linux_arm64.txt": "linux_aarch64",
+                            "requirements.linux_x86_64.txt": "linux_x86_64",
+                        },
+                        experimental_index_url = "pypi.org",
+                    ),
+                ],
+            ),
+            read = lambda x: {
+                "requirements.linux_arm64.txt": """\
+package==0.7.0 \
+    --hash=sha256:4dd8924f171ed73a4f1a6191e2f800ae1745069989b69fabc45593d6b6504003 \
+    --hash=sha256:62833036cbaf4641d66ae94c61c0446890a91b2c0d153946583a0ebe04877a76
+""",
+                "requirements.linux_x86_64.txt": """\
+package[extra]==0.7.0 \
+    --hash=sha256:62833036cbaf4641d66ae94c61c0446890a91b2c0d153946583a0ebe04877a76
+""",
+            }[x],
+        ),
+        available_interpreters = {
+            "python_3_12_host": "unit_test_interpreter_target",
+        },
+        minor_mapping = {"3.12": "3.12.11"},
+        simpleapi_download = lambda *_, **__: {
+            "package": parse_simpleapi_html(
+                url = "https://example.com/package",
+                content = """
+<a href="package-0.7.0.tar.gz#sha256=4dd8924f171ed73a4f1a6191e2f800ae1745069989b69fabc45593d6b6504003">package-0.7.0.tar.gz</a>
+<a href="package-0.7.0-py3-none-any.whl#sha256=62833036cbaf4641d66ae94c61c0446890a91b2c0d153946583a0ebe04877a76">package-0.7.0-py3-none-any.whl</a>
+""",
+            ),
+        },
+    )
+
+    pypi.exposed_packages().contains_exactly({"pypi": ["package"]})
+    # TODO(hartikainen): Check these expectations.
+    pypi.hub_whl_map().contains_exactly({"pypi": {
+        "package": {
+            "pypi_312_package_py3_none_any_62833036": [
+                whl_config_setting(
+                    # TODO(hartikainen): I think all these platforms use the same `.whl`
+                    # and thus all three platforms should be included in the same
+                    # `target_platforms` here?
+                    target_platforms = ["cp312_linux_aarch64", "cp312_linux_x86_64"],
+                    version = "3.12",
+                ),
+            ],
+        },
+    }})
+    pypi.whl_libraries().contains_exactly({
+        # The error stems here. We have two different platforms pointing to the same
+        # universal wheel, both just with different extras. The key clashes and probably
+        # needs the extras to be included in it.
+        "pypi_312_package_py3_none_any_62833036": {
+            "dep_template": "@pypi//{name}:{target}",
+            "download_only": True,
+            "experimental_target_platforms": ["linux_aarch64", "linux_x86_64"],
+            "filename": "package-0.7.0-py3-none-any.whl",
+            "python_interpreter_target": "unit_test_interpreter_target",
+            # NOTE(hartikainen): Perhaps this is part of the problem?
+            # This should say `package[extra]==0.7.0` for `linux_x86_64` platform and
+            # `package==0.7.0` for `linux_aarch64`
+            "requirement": "package[extra]==0.7.0",
+            "sha256": "62833036cbaf4641d66ae94c61c0446890a91b2c0d153946583a0ebe04877a76",
+            "urls": ["https://example.com/package-0.7.0-py3-none-any.whl"],
+        },
+    })
+    pypi.whl_mods().contains_exactly({})
+
+_tests.append(_test_simple_multiple_platforms_with_extras)
+
 def _test_simple_with_markers(env):
     pypi = _parse_modules(
         env,