Enable non cgo build

[tarakby]

Previously, cgo is required to build the module.

However:

• not all primitives supported in the module require cgo. Only the primitives based on the BLS12-381 do. Applications not requiring these primitives should be able to build without cgo.
• some applications requiring one or a few of the cgo primitives may want to build without cgo in some cases, and not the run the binary. These applications would want all the exported functions of the modules to remain exported with or without cgo.

This PR solves both issues above:

• it enables building without cgo: this requires CGO_ENABLED=0 and using the build tag no_cgo.
• export all public functions of the repo when building without cgo. Any of the non-supported functions panics when called.

Changes to CI jobs:

• add lint job for building without cgo
• test the module when building without cgo (including making sure non supported functions panic)
• test non allowed build combinations (in particular building without cgo and fogetting the no-cgo tag)
• reorganize ci jobs

[turbolent]

Nice!

[turbolent]

Nice! LGTM 👍

[turbolent]

Don't know, but wanted to flag: The build is green, but a GH action is flagging issues at the bottom of the PR: https://github.com/onflow/crypto/pull/8/files#file-sign-go-L77

[jribbink]

LGTM

[tarakby]

Don't know, but wanted to flag: The build is green, but a GH action is flagging issues

Good flag. This is because of a new check I added to CI in 65daa31. The test checks that the build with incorrect flags fail. The errors are expected but I would prefer that they don't show in every PR 🤔

[tarakby]

re displayed errors while CI pass : errors are not displayed anymore by disabling the go matcher in the workflow 9c0feda