cmd/hi: add integration test runner CLI tool (#2648)

* cmd/hi: add integration test runner CLI tool

Add a new CLI tool 'hi' for running headscale integration tests
with Docker automation. The tool replaces manual Docker command
composition with an automated solution.

Features:
- Run integration tests in golang:1.24 containers
- Docker context detection (supports colima and other contexts)
- Test isolation with unique run IDs and isolated control_logs
- Automatic Docker image pulling and container management
- Comprehensive cleanup operations for containers, networks, images
- Docker volume caching for Go modules
- Verbose logging and detailed test artifact reporting
- Support for PostgreSQL/SQLite selection and various test flags

Usage: go run ./cmd/hi run TestPingAllByIP --verbose

The tool uses creachadair/command and flax for CLI parsing and
provides cleanup subcommands for Docker resource management.

Updates flake.nix vendorHash for new Go dependencies.

* ci: update integration tests to use hi CLI tool

Replace manual Docker command composition in GitHub Actions
workflow with the new hi CLI tool for running integration tests.

Changes:
- Replace complex docker run command with simple 'go run ./cmd/hi run'
- Remove manual environment variable setup (handled by hi tool)
- Update artifact paths for new timestamped log directory structure
- Simplify command from 15+ lines to 3 lines
- Maintain all existing functionality (postgres/sqlite, timeout, test patterns)

The hi tool automatically handles Docker context detection, container
management, volume mounting, and environment variable setup that was
previously done manually in the workflow.

* makefile: remove test integration

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

---------

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

Makefile

@@ -24,17 +24,6 @@ dev: lint test build
 test:
 	gotestsum -- -short -race -coverprofile=coverage.out ./...
 
-test_integration:
-	docker run \
-		-t --rm \
-		-v ~/.cache/hs-integration-go:/go \
-		--name headscale-test-suite \
-		-v $$PWD:$$PWD -w $$PWD/integration \
-		-v /var/run/docker.sock:/var/run/docker.sock \
-		-v $$PWD/control_logs:/tmp/control \
-		golang:1 \
-		go run gotest.tools/gotestsum@latest -- -race -failfast ./... -timeout 120m -parallel 8
-
 lint:
 	golangci-lint run --fix --timeout 10m