ci: use go tool (#25)

## Description

Tool versions were not pinned to the repository: this caused issues with upgrades.

## Changes

- Use `go tool` for `checkmake`, `gremlins`, `golangci-lint`, `godoc` and `govulncheck`.

### Design Decisions

## Checklist

- [x] Tests pass
- [x] Docs updated

Reviewed-on: #25
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

Makefile

@@ -4,17 +4,13 @@ help: ## Show this help
 	@grep -E '^[a-zA-Z_-]+:.*##' $(MAKEFILE_LIST) | awk -F ':.*## ' '{printf "  %-15s %s\n", $$1, $$2}'
 
 install: ## Install dev tools
-	go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest
-	go install github.com/checkmake/checkmake/cmd/checkmake@latest
-	go install github.com/go-gremlins/gremlins/cmd/gremlins@latest
-	go install golang.org/x/tools/cmd/godoc@latest
-	go install golang.org/x/vuln/cmd/govulncheck@latest
+	go mod download
 
 test-unit: ## Run unit tests with coverage
 	go test ./... -cover -v
 
 test-mutation: ## Run mutation tests with gremlins
-	gremlins unleash
+	go tool gremlins unleash
 
 FUZZ_TIME ?= 30
 
@@ -27,10 +23,10 @@ test-fuzz: ## Run all fuzz tests for 30s each
 test: test-unit test-mutation test-fuzz ## Run all tests
 
 lint-go: ## Lint Go code
-	golangci-lint run ./...
+	go tool golangci-lint run ./...
 
 lint-makefile: ## Lint the Makefile
-	checkmake Makefile
+	go tool checkmake Makefile
 
 lint-markdown: ## Lint Markdown files
 	docker run --rm -v $(CURDIR):/workdir davidanson/markdownlint-cli2 "**/*.md"
@@ -39,7 +35,7 @@ lint: lint-go lint-makefile lint-markdown ## Lint all code
 
 docs: ## Serve godoc locally
 	@echo ">>> Visit: http://localhost:6060/pkg/$$(go list -m)"
-	godoc -http=:6060
+	go tool godoc -http=:6060
 
 clean: ## Clean build and test caches
 	go clean -cache -testcache