optimize text parser (#2144)

### What problem does this PR solve?


### Type of change

- [x] Performance Improvement

deepdoc/parser/txt_parser.py

@@ -33,14 +33,30 @@ class RAGFlowTxtParser:
     def parser_txt(cls, txt, chunk_token_num=128, delimiter="\n!?;。；！？"):
         if type(txt) != str:
             raise TypeError("txt type should be str!")
-        sections = []
-        for sec in re.split(r"[%s]+"%delimiter, txt):
-            if sections and sec in delimiter:
-                sections[-1][0] += sec
-                continue
-            if num_tokens_from_string(sec) > 10 * int(chunk_token_num):
-                sections.append([sec[: int(len(sec) / 2)], ""])
-                sections.append([sec[int(len(sec) / 2) :], ""])
+        cks = [""]
+        tk_nums = [0]
+
+        def add_chunk(t):
+            nonlocal cks, tk_nums, delimiter
+            tnum = num_tokens_from_string(t)
+            if tnum < 8:
+                pos = ""
+            if tk_nums[-1] > chunk_token_num:
+                cks.append(t)
+                tk_nums.append(tnum)
             else:
-                sections.append([sec, ""])
-        return sections
+                cks[-1] += t
+                tk_nums[-1] += tnum
+
+        s, e = 0, 1
+        while e < len(txt):
+            if txt[e] in delimiter:
+                add_chunk(txt[s: e + 1])
+                s = e + 1
+                e = s + 1
+            else:
+                e += 1
+        if s < e:
+            add_chunk(txt[s: e + 1])
+
+        return [[c,""] for c in cks]