Fix entry-point discovery and support deferred (PEP 563) annotations

[audivir]

I found two separate bugs while building a third-party converter plugin:

First, entry-point discovery was completely broken for all third-party plugins. It turns out that during the migration from pkg_resources to importlib.metadata, the code started using entry_points(name=group_name) instead of group=group_name. Because name filters a different field, anything under uplink.plugins.* was being silently ignored.

Second, get_arg_spec wasn't handling deferred annotations (PEP 563). If from __future__ import annotations was used, inspect.signature returned strings instead of actual objects, which broke the matching for Body(type=Model) and return types. This fixes #181.

Changes

• Fixed the filter in uplink/_extras.py to use group= instead of name=.
• Updated uplink/utils.py to use eval_str=True in inspect.signature (which is supported since we're on Python 3.10+).
• Added regression tests for both issues.

Testing

• Ran uv run pytest tests/ (all 411 passed).
• Verified manually with a real third-party converter: auto-discovery now works without explicit imports, and annotations work whether or not from __future__ import annotations is present.

Fixes #181.