* depends: Use `_staging_dir` in `bls-dash` and `immer` packages the way it's suggested in `depends/packages.md`
* depends: Do not build static binaries in `bls-dash` package
* build: detect the presence of libgmp before generating Makefile
* depends: add arximboldi/immer@v0.6.2 as a package and add detection
* depends: remove immer from source tree, build using package only
* Drop immer refs from tools
Co-authored-by: UdjinM6 <UdjinM6@users.noreply.github.com>