fix(quickadapter): honor unlimited trade sentinel (#184)

fix(quickadapter): honor unlimited trade sentinel (#184)

* fix(quickadapter): honor unlimited trade sentinel

* refactor(quickadapter): unify unlimited trade sentinel detection

Consolidate the three divergent unlimited max_open_trades predicates into a
single _is_unlimited_open_trades helper, honoring both the raw -1 sentinel and
its runtime-normalized float("inf") form (matching Freqtrade's own
config_validation idiom).

Behavior is preserved for every schema-legal max_open_trades value (config
schema minimum is -1): the sole formal divergence is that max_open_trades < -1,
already rejected by Freqtrade at config load, is no longer treated as unlimited
by max_open_trades_per_side. Also makes the confirm_trade_entry guard reject
the +inf form explicitly instead of relying on IEEE finite >= inf semantics.

* refactor(quickadapter): harmonize unlimited max_open_trades helper

Rename _is_unlimited_open_trades to _is_unlimited_max_open_trades (and the
local flag) for terminological precision with max_open_trades and
max_open_trades_per_side, and widen its parameter annotation to int | float to
match the is_trade_duration_valid precedent. No behavior change.