Enforce Go style rules across codebase

Apply five style rules: convert iota string enums to typed
string constants, replace errors.As with errors.AsType,
merge three-group imports into two groups, fix multiline
parameter/argument formatting, and replace fmt.Sprintf URL
construction with net/url.

Signed-off-by: Émile Ré <emile@probo.com>

pkg/llm/bedrock/provider.go

@@ -329,9 +329,8 @@ func mapStopReason(reason types.StopReason) llm.FinishReason {
 }
 
 func mapError(err error) error {
-	var respErr *smithyhttp.ResponseError
-	if !errors.As(err, &respErr) {
-		// Check for common error types by message content.
+	respErr, ok := errors.AsType[*smithyhttp.ResponseError](err)
+	if !ok {
 		msg := err.Error()
 		if strings.Contains(msg, "throttling") || strings.Contains(msg, "ThrottlingException") {
 			return &llm.ErrRateLimit{Err: err}