fix!: up-transitions no longer exit and re-enter the target ancestor

A transition whose target is already active (an ancestor of the
innermost active state) now unwinds only the subtree strictly below
the target. The target's entry/exit actions do not fire and its
default() does not re-descend — you cannot re-enter a state you never
left. The old behavior could loop infinitely when a child transitioned
to its own parent.

Self-transitions (target == innermost) and lateral transitions are
unchanged. See spec §2.6 and tests §T2.8 / T2.8b / T2.8c.

Also in this release:

* Full workspace justfile (check, test, coverage, mutants, pre-release)
* Unit tests covering all __private internals; `cargo mutants` now exits
  clean (38 caught, 178 unviable, 0 missed, 0 timeouts).
* .config/nextest.toml with slow-timeout/terminate-after so hung tests
  fail fast rather than wedging cargo-mutants runs.

BREAKING CHANGE: transition-to-ancestor semantics. Machines that relied
on the old re-entry behavior of up-transitions will observe different
exit/entry action sequences.

Cargo.toml

@@ -3,7 +3,7 @@ resolver = "2"
 members = ["hsmc", "hsmc-macros"]
 
 [workspace.package]
-version = "0.1.0"
+version = "0.2.0"
 edition = "2021"
 license = "MIT OR Apache-2.0"
 authors = ["Stephen Waits <steve@waits.net>"]