overhaul chain system

This made the code so fast, that the `board` benchmark became completely useless.
So that benchmark was removed.

Overall, we're looking at a futher 20% performance increase in `future_moves`

Cargo.toml

@@ -21,12 +21,8 @@ inherits = "release"
 # for profiling
 debug = true
 
-[features]
-bitvec = [ "dep:bitvec" ]
-
 [dependencies]
 arrayvec = "0.7"
-bitvec = { version = "1", optional = true }
 const_fn = "0.4"
 either = "1.13"
 indicatif = "0.17"
@@ -44,10 +40,6 @@ criterion = { version = "0.5", features = [ "html_reports" ] }
 name = "future_children"
 harness = false
 
-[[bench]]
-name = "board"
-harness = false
-
 [lints.rust]
 # fix weird warnings about `test` not being expected
 unexpected_cfgs = { level = "allow", check-cfg = ['cfg(test)'] }