fix(quickadapter): preserve valid partial-exit remainder (#118)

fix(quickadapter): preserve valid partial-exit remainder (#118)

Trigger the take-profit partial exit at freqtrade's executable current_exit_rate
instead of the entry-side current_rate, and size the partial-exit remainder so it
survives freqtrade's minimum-stake guard.

- Evaluate the take-profit trigger and the remaining position at current_exit_rate
  (the rate the exit actually fills at); the previous current_rate is the entry rate
  in this callback and could fire a long exit below its bid target (symmetric short).
- freqtrade passes min_entry_stake as min_stake but rejects the partial exit when the
  remaining value is below the larger min_exit_stake. Size the remainder against a
  proven upper bound min_exit_stake <= min_stake * max(current_exit_rate/current_entry_rate,
  1/(1-|stoploss|)) (holds for both the cost- and amount-driven minimum), with a small
  rounding margin, so the shrunk remainder clears the guard. Leverage cancels; amount
  precision and final validation are left to freqtrade.