fix: replace deprecated pandas fillna(method=) with ffill()/bfill() (#1987)

* fix: replace deprecated pandas fillna(method=) with ffill()/bfill()

  Replace deprecated fillna(method="ffill"/"bfill") calls with modern
  pandas ffill() and bfill() methods to fix FutureWarnings in pandas 2.x.

  Also includes black formatting fixes for compliance.

  This addresses the pandas deprecation warnings portion of issue #1981.
  Other issues (date parsing, type conversion, timezone handling) will be
  addressed in separate commits.

  Fixes:
  - Yahoo collector: 2 instances in calc_change() and adjusted_price()
  - BaoStock collector: 1 instance in calc_change()
  - Core utils: resam.py fillna operations
  - Backtest: profit_attribution.py stock data processing
  - High-freq ops: FFillNan and BFillNan operators
  - Position analysis: parse_position.py weight processing

  Partially addresses GitHub issue #1981

* lint with black

* lint with black

* limit minimum version of pandas

* limit minimum version of pandas

---------

Co-authored-by: Linlang <Lv.Linlang@hotmail.com>

pyproject.toml

@@ -27,7 +27,10 @@ license = { text = "MIT" }
 dependencies = [
   "pyyaml",
   "numpy",
-  "pandas>=0.24",
+  # Since version 1.1.0, pandas supports the ffill and bfill methods.
+  # Since version 2.1.0, pandas has deprecated the method parameter of the fillna method. 
+  # qlib has updated the fillna method in PR 1987 and limited the minimum version of pandas.
+  "pandas>=1.1",
   # I encoutered an Error that the set_uri does not work when downloading artifacts in mlflow 3.1.1;
   # But earlier versions of mlflow does not have this problem.
   # But when I switch to 2.*.* version, another error occurs, which is even more strange...