fix: chanlun bi algorithm stuck in fractal trap during sustained trends

Fix find_bis() greedy algorithm terminating early when dense alternating
fractals cause gap=0 for every opposite-type fractal. The root cause was
blindly replacing start_fx with more extreme same-type fractals, pushing
right_kline_index forward and making subsequent gaps permanently 0.

Solution: add pending_opposite guard — when an opposite-type fractal fails
the gap check, freeze start_fx replacement until a valid bi is formed.

- Affects: sustained up/down trends with dense fractals (e.g. high-price stocks)
- 600519: 114 bi (ending 04-28) -> 142 bi (ending 05-27)
- 601088: 131 bi -> 147 bi (end date unchanged)
- New regression test: test_fractal_trap_regression
- Bump version to 1.7.1

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "easy-tdx"
-version = "1.7.0"
+version = "1.7.1"
 description = "通达信 TCP 协议行情数据客户端，支持在线行情、离线数据读取与写入同步"
 readme = "README.md"
 requires-python = ">=3.10"