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>

flake.nix

@@ -30,7 +30,7 @@
 
           # When updating go.mod or go.sum, a new sha will need to be calculated,
           # update this if you have a mismatch after doing a change to those files.
-          vendorHash = "sha256-dR8xmUIDMIy08lhm7r95GNNMAbXv4qSH3v9HR40HlNk=";
+          vendorHash = "sha256-8nRaQNwUDbHkp3q54R6eLDh1GkfwBlh4b9w0IkNj2sY=";
 
           subPackages = ["cmd/headscale"];