support post-release versions, public v1.15.0.post1 (#5)

Contributes to rapidsai/build-planning#57.

`libucx.load_library()` defined here tries to pre-load `libcuda.so` and
`libnvidia-ml.so`, to raise an informative error (instead of a cryptic
one from a linker) if someone attempts to use the libraries from this
wheel on a system without a GPU.

Some of the projects using these wheels, like `ucxx` and `ucx-py`, are
expected to be usable on systems without a GPU. See
rapidsai/ucx-py#1041 (comment).

To avoid those libraries needing to try-catch these errors, this
proposes the following:

* removing those checks and deferring to downstream libraries to handle
the non-GPU case
* modifying the build logic so we can publish patched versions of these
wheels like `v1.15.0.post1`

### Notes for Reviewers

Proposing starting with `1.15.0.post1` right away, since that's the
version that `ucx-py` will use. I'm proposing the following sequence of
PRs here (assuming downstream testing goes well):

1. this one
2. another changing the version to `1.14.0.post1`
3. another changing the version to `1.16.0.post1`

README.md

@@ -16,3 +16,9 @@ While this approach can still be problematic if other libraries loaded on the sy
 
 UCX wheels in this repository are built by using a custom build command for setuptools to trigger the build of the UCX library.
 The library is then bundled and installed directly into the output directories.
+
+`{major}.{minor}.{patch}` versions of this library exactly correspond to versions of UCX.
+For example, `libucx==1.16.0` contains libraries built from https://github.com/openucx/ucx/releases/tag/v1.16.0.
+
+When the packaging logic itself changes, post-release versions like `libucx==1.16.0.post1` are released.
+See "Post-releases" in the Python packaging docs ([link](https://packaging.python.org/en/latest/specifications/version-specifiers/#post-releases)) for details.

VERSION

@@ -1 +1 @@
-1.16.0
+1.15.0.post1

python/libucx/libucx/load.py

@@ -34,22 +34,6 @@
 ]
 
 def load_library():
-    # First validate if libcuda.so and libnvidia-ml.so are present. These cannot be
-    # bundled, so we want to provide the user with a reasonable error if they are not
-    # available rather than a loader error on import.
-    try:
-        ctypes.CDLL("libcuda.so.1", ctypes.RTLD_GLOBAL)
-    except OSError:
-        raise RuntimeError("The CUDA driver library libcuda.so.1 was not found "
-                      "on your system. This library cannot be provided by the libucx "
-                      "wheel and must be installed separately.")
-
-    try:
-        ctypes.CDLL("libnvidia-ml.so.1", ctypes.RTLD_GLOBAL)
-    except OSError:
-        raise RuntimeError("The library libnvidia-ml.so.1 was not found on your "
-                      "system. This library cannot be provided by the libucx wheel and "
-                      "must be installed separately.")
 
     # Dynamically load libucx.so. Prefer a system library if one is present to
     # avoid clobbering symbols that other packages might expect, but if no

python/libucx/pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
 build-backend = "setuptools.build_meta"
 requires = [
+    "packaging",
     "setuptools>=64.0.0",
     "wheel",
 ]

python/libucx/setup.py

@@ -5,6 +5,7 @@
 import os
 import tempfile
 import glob
+import packaging.version
 
 
 @contextmanager
@@ -22,13 +23,17 @@ def run(self):
         super().run()
 
         with open("VERSION") as f:
-            version = f.read().strip()
+            package_version = f.read().strip()
+
+        # strip off any other non-UCX version components, like ".post1"
+        ucx_semver = packaging.version.parse(package_version).base_version
+        ucx_tag = f"v{ucx_semver}"
 
         install_prefix = os.path.abspath(os.path.join(self.build_lib, "libucx"))
 
         with tempfile.TemporaryDirectory() as tmpdir:
             with chdir(tmpdir):
-                subprocess.run(["git", "clone", "-b", f"v{version}", "https://github.com/openucx/ucx.git", "ucx"])
+                subprocess.run(["git", "clone", "-b", f"{ucx_tag}", "https://github.com/openucx/ucx.git", "ucx"])
                 with chdir("ucx"):
                     subprocess.run(["./autogen.sh"])
                     subprocess.run(["./contrib/configure-release",