FMD Sliding Window Algorithm has an edge case bug

[cronokirby]

penumbra/crates/core/component/shielded-pool/src/fmd.rs

Line 110 in e13cd3b

Precision::new(1u8).expect("1 is a valid precision")

In the case that there have been an estimated 0 clues over the past window, the targeted precision should be 0 (detect all clues) and not 1 (detect 50% of all clues).

One way to solve this in a non-consensus-breaking way is to add a flag to the algorithm in protobuf which will enable the fix here.

Also, this being wrong shouldn't cause clients to break, only that they use a sub-optimal precision for when transactions start up again.