Large amounts in the XRebalancer / XMoveFunds log lines were
unbroken digit runs (delivered 18851040 msat); grep-heavy log
sessions kept miscounting them. Add Util::Str::group_digits,
which renders an integer with an underscore every three digit
places (18_851_040), matching the digit grouping
clboss-xrebalance-view and the other contrib tools already
print.
Applied to the amounts that get large:
- XRebalancer cycle line (derived N, request)
- XRebalancer transfer-done line (delivered, fee)
- XMoveFunds planning line (amount, maxfee)
- XMoveFunds 204 summary and fee-picture diagnostics
(alloc_fee, required_out)
- XMoveFunds per-part budget refusals (would deliver)
- format_route_fees per-hop table (in/out/fee)
Counts, ppm values, and cltv deltas stay plain. Signed
overload handles the int64 call sites (INT64_MIN-safe).
New tests/util/test_str covers both overloads and the
boundary cases.
