arm64,purego: field arithmetic mul for arm64 and cleanup build tags (#…

…257)

* feat: remove special amd64_adx build tag path

* feat: get rid of adx build tag for e2

* docs: add generator mul decision strategy docs

* feat: generate unoptimized CIOS as default fallback

* feat: one more step towards purego vs amd64

* feat: added purego build tag for field arithmetic

* feat: replaced x86 optimized purego code with arm64 optimized

* docs: generate mul doc for field arithmetic

* docs: move generator mul doc to template

* build: ensure we run test with purego build tag

* style: update typo in comments

.github/workflows/pr.yml

@@ -68,7 +68,9 @@ jobs:
     - name: install deps
       run: go install golang.org/x/tools/cmd/goimports@latest && go install github.com/klauspost/asmfmt/cmd/asmfmt@latest
     - name: Test
-      run: go test -p=1 -v -timeout=30m ./...
+      run: |
+        go test -p=1 -v -timeout=30m ./...
+        go test -p=1 -tags=purego -v -timeout=30m ./...
     - name: Test (32 bits & race)
       if: (matrix.os == 'ubuntu-latest') && (matrix.go-version == '1.18.x')
       run: |