P3: depreciation straight-line by days through the final month, schedules by day (defects 22, 9, D-37)

The final month takes what the months before leave, spread over its days;
a disposed asset stops on its disposal day. A skipped month is caught up
in the month the run is made; a reversed run un-posts its month. New
schedules spread by day; equal-months schedules must start on the 1st.
Amounts round to the currency's own minor unit. Kani and Lean proofs; an
exhaustive search over runs, reversals and disposals.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-core/tests/invariants.rs

@@ -1257,6 +1257,7 @@ fn id_allocators_predict_the_next_id_and_never_repeat() {
         months: 12,
         balance_account: c.equipment,
         pl_account: c.rent,
+        convention: ledger_core::ScheduleConvention::MonthlyEven,
     };
     let mut seen = Vec::new();
     for n in ["a", "b"] {