v5.8.1

Nuthatch 5.8.1 refuses to reopen a store, or reuse its segments, after an event's indexed parameters
have moved. There is no storage migration, and no nest's NID or registry hash changes.

A swapped indexed parameter is refused, not misread

An event's indexed markers decide which values come from topics and which from data. Swapping which
parameter is indexed, at the same arity, keeps topic0 and the registry hash, so a reopened store and
a compatible update reusing the old version's sealed segments trusted rows decoded under the other layout (#2157). A store
now records each event table's indexed positions. A mismatch at start refuses and names the table and
both position lists; segment reuse declines rather than copying. A store from before 5.8.1 has no
record, adopts the current layout on its first start and starts as before.

No Python in the tree

The repository's test fixtures, CI helpers, eval runners and the webhook receiver example were
Python. They are now Rust (tools/fixture-rpc, eval/runner, examples/webhooks) or bash with jq
(#2294). The shipped binary is unchanged by this.

Compatibility and upgrade

Replace the binary and restart. A 5.8.0 store is used as it is.