Add precompiled NIFs for freebsd (#618)

* Add freebsd as target for precomp NIFs

* Use existing target

* Use ubuntu as OS and make use of cross

* Set cross version to v0.2.5

The default is cross v0.2.4 which was created in Juli of 2022 [0]. The
patch to add libmemstat [1] was created in December of 2022, so we need
a newer version of cross.

[0] https://github.com/cross-rs/cross/pkgs/container/x86_64-unknown-freebsd/28076628?tag=0.2.4
[1] cross-rs/cross#1166

* Use ubuntu-22.04 for freebsd target

* Re-enable all disabled targets

* Use ubuntu-22.04 for all cross based targets

* Revert to use ubuntu-20.04 for existing targets

This introduces a new variable `cross-version` which defaults to v0.2.4
and is set to v0.2.5 for freebsd.

It is required because cross v0.2.5 fails to build on ubuntu-20.04.

* Add freebsd to list of targets

.github/workflows/release.yml

@@ -36,6 +36,7 @@ jobs:
           - { target: riscv64gc-unknown-linux-gnu, os: ubuntu-20.04, use-cross: true, disable-polars-json-feature: true }
           - { target: x86_64-pc-windows-gnu, os: windows-2019 }
           - { target: x86_64-pc-windows-msvc, os: windows-2019 }
+          - { target: x86_64-unknown-freebsd, os: ubuntu-22.04, use-cross: true, cross-version: v0.2.5 }
 
     steps:
       - name: Checkout source code
@@ -81,6 +82,7 @@ jobs:
           target: ${{ matrix.job.target }}
           nif-version: ${{ matrix.nif }}
           use-cross: ${{ matrix.job.use-cross }}
+          cross-version: ${{ matrix.job.cross-version || 'v0.2.4' }}
           project-dir: "native/explorer"
 
       - name: Artifact upload

lib/explorer/polars_backend/native.ex

@@ -22,6 +22,7 @@ defmodule Explorer.PolarsBackend.Native do
       x86_64-pc-windows-gnu
       x86_64-unknown-linux-gnu
       x86_64-unknown-linux-musl
+      x86_64-unknown-freebsd
     ),
     mode: mode,
     force_build: System.get_env("EXPLORER_BUILD") in ["1", "true"]