[REF] stock_account: move's value and exceptions

Update the value on the moves when exceptions happen (unlock and edit,
negative stock).

This is a preliminary work to bring the valuation at date wizard to v11.

We also update the value on moves in the standard cost method to stay
consistent.

- `_run_fifo` now returns the used value in the negative stock case
- we simplify the `_fifo_vacuum` method so that the `remaining_value`
  always represent the not yet compensated value
- we adapt the tests to reflect theses changes ; the value is not the
  initial valued amount but is updated upon exceptions