Each feature has a name, and says when deprecation begins and ends.
There's an API coming to allow you to re-enable on a per-feature basis
even if it's ended (as long as it's not been removed from the code ofc!).
Default end is 6 months after deprecation, i.e. we complain about it
at that point, if we can detect its use.
e.g, a standard deprecation in v24.05:
v24.02: allowed
v24.02 with mods: allowed
master after v24.02: allowed unless deprecated APIs disabled.
v24.05: allowed unless deprecated APIs disabled.
v24.08: allowed unless deprecated APIs disabled.
v24.11: allowed unless deprecated APIs disabled, but logs at BROKEN level.
v25.02: allowed only if --i-promise-to-fix-broken-api-user=FEATURE.
v25.05: code is actually removed.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
