Missing proxy support in AWSCRTHTTPClient → blocks aws_sdk_bedrock_runtime in private VPCs

Please let me know if I'm missing something When using `aws_sdk_bedrock_runtime` to invoke Amazon Nova Sonic in a private VPC (us-west-2), the HTTP stack cannot honor HTTP_PROXY / HTTPS_PROXY because the CRT-based HTTP client does not expose any proxy configuration.

This makes `aws_sdk_bedrock_runtime` unusable in environments where all outbound internet access must go through a proxy (e.g., ECS Fargate in private subnets without NAT or VPC endpoint).

**Application creates a Bedrock client:**

```
crt_http_client = create_crt_http_client(PROXY_URL if not IS_DEV else None)

bedrock_nova_sonic_config = BedrockConfig(
endpoint_uri=f"https://bedrock-runtime.{ONLY_AVAILABLE_REGION_FOR_AWS_NOVA}.amazonaws.com",
region=ONLY_AVAILABLE_REGION_FOR_AWS_NOVA,
aws_credentials_identity_resolver=EnvironmentCredentialsResolver(),
http_auth_scheme_resolver=HTTPAuthSchemeResolver(),
http_auth_schemes={"aws.auth#sigv4": SigV4AuthScheme()},
http_client=crt_http_client,
)
bedrock_client = BedrockRuntimeClient(bedrock_nova_sonic_config)
```

**That `crt_http_client` is always an instance of:**
`from smithy_http.aio.crt import AWSCRTHTTPClient`

**Which in turn requires AWSCRTHTTPClientConfig:**
```
class AWSCRTHTTPClientConfig(http_interfaces.HTTPClientConfiguration):
def __post_init__(self) -> None:
_assert_crt()
And the actual client implementation:
class AWSCRTHTTPClient(http_aio_interfaces.HTTPClient):
_HTTP_PORT = 80
_HTTPS_PORT = 443

def __init__(self, eventloop=None, client_config=None):
_assert_crt()
self._config = client_config or AWSCRTHTTPClientConfig()
self._eventloop = eventloop or _AWSCRTEventLoop()
self._client_bootstrap = self._eventloop.bootstrap
self._tls_ctx = crt_io.ClientTlsContext(crt_io.TlsContextOptions())
self._socket_options = crt_io.SocketOptions()
self._connections = {}
```

**The only config type available is:**

```
@dataclass(kw_only=True)
class HTTPClientConfiguration:
"""Client-level HTTP configuration.

:param force_http_2: Whether to require HTTP/2.
"""
force_http_2: bool = False

```
There is no field for proxy configuration, nor does **AWSCRTHTTPClient** internally handle HTTP_PROXY / HTTPS_PROXY.
The underlying call in _build_new_connection goes directly to crt_http.HttpClientConnection.new(...) with just host_name, port, socket_options, and tls_connection_options.

Please add first-class proxy support to smithy-http’s `AWSCRTHTTPClient`.

从 smithy-http 中的 AWSCRTHTTPClientConfig 和 AWSCRTHTTPClient 开始，然后跟踪 _build_new_connection 及其对 crt_http.HttpClientConnection.new(...) 的调用。确定应如何表示代理配置，以及如何通过 CRT 客户端传递该配置。完成标准是 AWSCRTHTTPClient 能够为私有 VPC 中的 Bedrock 客户端使用 HTTP_PROXY/HTTPS_PROXY 或等效的一等代理设置。

由索引模型根据 Issue 内容生成。