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/Cargo.toml

@@ -22,8 +22,12 @@ workspace = true
 [dev-dependencies]
 criterion = "0.8.2"
 proptest = "1"
-# bookspec examples are TOML (tests/bookspec.rs).
+# bookspec examples are TOML (tests/bookspec.rs), run on the engine's own
+# store (a dev-dependency only: the store depends on this crate), each in
+# a directory of its own.
 toml = "1"
+ledger-store = { path = "../ledger-store" }
+tempfile = "3"
 
 [[bench]]
 name = "books"