Fix polkadot-node-core-pvf-prepare-worker build with jemalloc (#1315)

* Fix polkadot-node-core-pvf-prepare-worker build with jemalloc

The jemalloc feature on polkadot-node-core-pvf-prepare-worker depended
on some feature gated code in polkadot-node-core-pvf-common but there
way no way to enable this feature gate.

This commit adds the feature and makes prepare-worker enable it.

* More jemalloc-allocator fixes

* Fix jemalloc-allocator feature dep

* Run `zepter format features`

---------

Co-authored-by: Marcin S <marcin@realemail.net>