Fix: Increase default chunk_token_num from 128 to 512 in parser config (#8753)

### What problem does this PR solve?

Updated the default `chunk_token_num` value in `api_utils.py` and
`validation_utils.py` to 512 to accommodate larger text chunks. Adjusted
corresponding test cases in HTTP and SDK API tests to reflect this
change.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/utils/api_utils.py

@@ -348,7 +348,7 @@ def get_parser_config(chunk_method, parser_config):
     if not chunk_method:
         chunk_method = "naive"
     key_mapping = {
-        "naive": {"chunk_token_num": 128, "delimiter": r"\n", "html4excel": False, "layout_recognize": "DeepDOC", "raptor": {"use_raptor": False}},
+        "naive": {"chunk_token_num": 512, "delimiter": r"\n", "html4excel": False, "layout_recognize": "DeepDOC", "raptor": {"use_raptor": False}},
         "qa": {"raptor": {"use_raptor": False}},
         "tag": None,
         "resume": None,

api/utils/validation_utils.py

@@ -363,7 +363,7 @@ class GraphragConfig(Base):
 class ParserConfig(Base):
     auto_keywords: int = Field(default=0, ge=0, le=32)
     auto_questions: int = Field(default=0, ge=0, le=10)
-    chunk_token_num: int = Field(default=128, ge=1, le=2048)
+    chunk_token_num: int = Field(default=512, ge=1, le=2048)
     delimiter: str = Field(default=r"\n", min_length=1)
     graphrag: GraphragConfig | None = None
     html4excel: bool = False