Add pulp3 client [RHELDST-38334]

Added 'raw' clienit for pulp3 API for basic operations required for:
* repository creation, content search (limited), creation of publication
  and distribution and some other functions like polling tasks.
* written as async using anyio with trio backend, using httpx requests and
  tenacity for retries
* it is expected that this code will undergo further optimization and
  refactoring with higher level of abstraction

Assisted-by: Claude Code

Author: rbikar

docs/api/client_pulp3.rst

@@ -0,0 +1,15 @@
+API: client for Pulp 3
+======================
+
+.. autoclass:: pubtools.pulplib.Pulp3Client
+   :members:
+
+Errors
+------
+
+.. autoclass:: pubtools.pulplib.Pulp3Exception
+   :members:
+
+.. autoclass:: pubtools.pulplib.Pulp3TaskException
+   :members:
+        

docs/index.rst

@@ -8,6 +8,7 @@ A Pulp library for publishing tools.
    :caption: Contents:
 
    api/client
+   api/client_pulp3
    api/pulpcore
    api/yum
    api/files

requirements.txt

@@ -8,3 +8,6 @@ frozendict; python_version >= '3.6'
 pubtools>=0.3.0
 monotonic; python_version < '3.3'
 defusedxml
+httpx
+tenacity
+anyio[trio]

src/pubtools/pulplib/__init__.py

@@ -1,4 +1,5 @@
 from ._impl.client import Client, PulpException, TaskFailedException, CopyOptions
+from ._impl.client_pulp3 import Pulp3Client
 from ._impl.criteria import Criteria, Matcher
 from ._impl.page import Page
 from ._impl.model import (

src/pubtools/pulplib/_impl/client_pulp3/__init__.py

@@ -0,0 +1,2 @@
+from .client import Pulp3Client
+from .errors import Pulp3Exception, Pulp3TaskException