feat: merge datetime fields in DataFrame output, hide MinuteBar internal fields

- K-line: daily+ periods output 'date' only, minute periods output 'datetime'
- Transactions (tick-by-tick): combine date param + hour/minute into 'datetime'
- XdxrRecord, HistoricalFundFlow: year/month/day merged to 'date'
- MinuteBar: rename unknown_1 to _unknown_1 (hidden from DataFrame)
- MinuteBar: add datetime column computed from bar index (A-share 240-bar pattern)
- get_minute_time_data: use history endpoint only (current-day endpoint broken in pytdx too)
- Update all examples to reflect new DataFrame column names

examples/07_block/block_info.py

@@ -6,16 +6,9 @@
   'block_fg.dat' - 风格板块
 """
 
-import pandas as pd
 from easy_tdx import TdxClient
 
 with TdxClient.from_best_host() as c:
-    blocks = c.get_block_info("block_gn.dat")
-    df = pd.DataFrame([{
-        "板块名称": b.name,
-        "分类": b.category,
-        "成分股数": b.count,
-        "代码(前5)": ", ".join(b.codes[:5]),
-    } for b in blocks])
+    df = c.get_block_info("block_gn.dat")
     print(f"概念板块，共 {len(df)} 个:")
-    print(df.head(20).to_string(index=False))
+    print(df[["name", "category", "count"]].head(20).to_string(index=False))