Validating large pickings is much faster

Commit message

[PERF] stock: batch stock.move.line writes in _inverse_picked

_inverse_picked wrote move.move_line_ids.picked one move at a time,
so button_validate on a picking with a couple thousand moves issued
one stock.move.line write per move. Each write re-triggers
base_automation's write hook, which recompiles every active rule's
domain on stock.move.line (safe_eval + compile, never cached).
Measured 8s of an 8.2s button_validate spent there on such a picking.

Split the moves into picked and not picked, then write each group's
move_line_ids once. Same end state, same records touched, two write
calls instead of one per move.

Benchmark, 2000 stock.move (1000 picked) + 2000 stock.move.line, one
active base_automation on_create_or_write rule on stock.move.line,
fresh 17.0 database with no demo data:

    before: 3.001s, 4012 queries
    after:  0.269s, 16 queries

11x faster, 250x fewer queries.