fix(pydantic): unconditional TypeAdapter import — eliminate NameError window

_get_adapter and the TypeError fallback inside PydanticDecoder.decode both
referenced TypeAdapter as a bare name. The name was bound only under
`if import_checker.is_pydantic_installed:`. If a test reloaded the module
with the flag patched to False, TypeAdapter was undefined and subsequent
calls raised NameError instead of the documented ImportError.

Hoist `from pydantic import TypeAdapter` unconditionally. The module is
gated upstream by client.py:_default_pydantic_decoder(), which raises
ImportError before this module is loaded when pydantic is absent — there
is no real-world path that loads pydantic.py without pydantic available.

Update the module docstring to reflect the new contract.

Closes audit Low finding (pydantic.py:15-16, 27, 43) from
planning/audit/2026-06-07-deep-audit.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: lesnik512

src/httpware/decoders/pydantic.py

@@ -1,19 +1,20 @@
 """PydanticDecoder — module-level cached TypeAdapter adapter for ResponseDecoder.
 
-Requires the `pydantic` extra: `pip install httpware[pydantic]`. Importing this
-module without the extra works (the `pydantic` import is guarded by a
-`find_spec` check), but instantiating the decoder raises `ImportError` with the
+Requires the `pydantic` extra: `pip install httpware[pydantic]`. The optional-extras
+gate is enforced upstream — `client.py:_default_pydantic_decoder()` raises
+ImportError when pydantic is absent, so this module is never imported in that
+path. Tests simulating "pydantic not installed" patch
+`import_checker.is_pydantic_installed=False` at runtime, after this module is
+already loaded; `PydanticDecoder.__init__` then raises ImportError with the
 install hint.
 """
 
 import functools
 from typing import TypeVar
 
-from httpware._internal import import_checker
-
+from pydantic import TypeAdapter
 
-if import_checker.is_pydantic_installed:
-    from pydantic import TypeAdapter
+from httpware._internal import import_checker
 
 
 MISSING_DEPENDENCY_MESSAGE = (