Fix Python bindings build with recent hatchling releases

`hatchling` validates that `project.readme` resolves inside the project
directory, so our `readme = "../../README.md"` now aborts every build of
the Python bindings with:

    ValueError: Readme path must be within the project directory: ../../README.md

This breaks the `check-python` CI job as well as `python_build_wheel.sh`.

Rather than duplicating the README into `bindings/python`, declare
`readme` dynamic and read the repository README from a custom metadata
hook, which hands it over as literal text and hence skips the path
validation. The resulting wheel metadata is byte-identical to what we
published before.

This commit was written with AI assistance.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: vincenzopalazzo

bindings/python/hatch_build.py

@@ -1,4 +1,16 @@
+import os
+
 from hatchling.builders.hooks.plugin.interface import BuildHookInterface
+from hatchling.metadata.plugin.interface import MetadataHookInterface
+
+
+class CustomMetadataHook(MetadataHookInterface):
+    # Hatchling refuses a `readme` path outside the project directory, so we read the
+    # repository README ourselves and hand it over as literal text instead.
+    def update(self, metadata):
+        readme_path = os.path.join(self.root, os.pardir, os.pardir, "README.md")
+        with open(readme_path, encoding="utf-8") as f:
+            metadata["readme"] = {"content-type": "text/markdown", "text": f.read()}
 
 
 class CustomBuildHook(BuildHookInterface):

bindings/python/pyproject.toml

@@ -9,7 +9,7 @@ authors = [
   { name="Elias Rohrer", email="dev@tnull.de" },
 ]
 description = "A ready-to-go Lightning node library built using LDK and BDK."
-readme = "../../README.md"
+dynamic = ["readme"]
 requires-python = ">=3.8"
 classifiers = [
     "Topic :: Software Development :: Libraries",
@@ -27,6 +27,8 @@ classifiers = [
 [dependency-groups]
 dev = ["requests"]
 
+[tool.hatch.metadata.hooks.custom]
+
 [tool.hatch.build.targets.wheel]
 packages = ["src/ldk_node"]