[api] Fix HELPER_LOG format mismatch and remove unused is_varint64 codegen field

- Cast msg_size/type_varint.value to uint32_t in HELPER_LOG to match PRIu32
  format (proto_varint_value_t is uint64_t on BLE builds)
- Remove unused is_varint64 field from api_protobuf.py TypeInfo classes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

script/api_protobuf/api_protobuf.py

@@ -193,7 +193,6 @@ class TypeInfo(ABC):
         return f"case {self.number}: this->{self.field_name} = {content}; break;"
 
     decode_varint = None
-    is_varint64 = False
 
     @property
     def decode_length_content(self) -> str:
@@ -463,7 +462,6 @@ class Int64Type(TypeInfo):
     cpp_type = "int64_t"
     default_value = "0"
     decode_varint = "static_cast<int64_t>(value)"
-    is_varint64 = True
     encode_func = "encode_int64"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -484,7 +482,6 @@ class UInt64Type(TypeInfo):
     cpp_type = "uint64_t"
     default_value = "0"
     decode_varint = "value"
-    is_varint64 = True
     encode_func = "encode_uint64"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -1286,7 +1283,6 @@ class SInt64Type(TypeInfo):
     cpp_type = "int64_t"
     default_value = "0"
     decode_varint = "decode_zigzag64(value)"
-    is_varint64 = True
     encode_func = "encode_sint64"
     wire_type = WireType.VARINT  # Uses wire type 0
 
@@ -1624,10 +1620,6 @@ class RepeatedTypeInfo(TypeInfo):
         """
         return self._ti.wire_type
 
-    @property
-    def is_varint64(self):
-        return self._ti.is_varint64
-
     @property
     def decode_varint_content(self) -> str:
         # Pointer fields don't support decoding