Support aws.protocoltests.json10#JsonRpc10

[crisidev]

To support this model we need:

• Properly cast BlobShape inside constrained unions:

diff --git a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/parse/JsonParserGenerator.kt b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/parse/JsonParserGenerator.kt
index dd7255e47..2389fc89c 100644
--- a/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/parse/JsonParserGenerator.kt
+++ b/codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/parse/JsonParserGenerator.kt
@@ -276,7 +276,7 @@ class JsonParserGenerator(
             is StringShape -> deserializeString(target)
             is BooleanShape -> rustTemplate("#{expect_bool_or_null}(tokens.next())?", *codegenScope)
             is NumberShape -> deserializeNumber(target)
-            is BlobShape -> deserializeBlob()
+            is BlobShape -> deserializeBlob(target)
             is TimestampShape -> deserializeTimestamp(target, memberShape)
             is CollectionShape -> deserializeCollection(target)
             is MapShape -> deserializeMap(target)
@@ -294,9 +294,10 @@ class JsonParserGenerator(
         }
     }
 
-    private fun RustWriter.deserializeBlob() {
+    private fun RustWriter.deserializeBlob(target: BlobShape) {
         rustTemplate(
-            "#{expect_blob_or_null}(tokens.next())?",
+            "#{expect_blob_or_null}(tokens.next())?#{ConvertFrom:W}",
+            "ConvertFrom" to typeConversionGenerator.convertViaFrom(target),
             *codegenScope,
         )
     }

• Disable generation of protocol tests until we can fully support them.