fix(go-alpm): add checks around nil pointers in Pkgcache

[Jguer]

Development Environment Updates:

• Added a Dockerfile in .devcontainer to set up a development container with Arch Linux, pre-installed tools (e.g., fish, git-delta, bat), and a non-root user configuration. (.devcontainer/Dockerfile)
• Added a devcontainer.json file to configure the development container, specifying the Dockerfile and installing the golang.go VS Code extension. (.devcontainer/devcontainer.json)

Code Improvements:

• Updated the PkgCache method in db.go to handle nil database pointers gracefully, returning an empty PackageList instead of causing a potential crash. (db.go)
• Simplified logging in the TestRevdeps function by replacing t.Logf with t.Log for non-formatted strings. (alpm_test.go)

Test Enhancements:

• Added comprehensive tests in db_test.go to cover database operations, including registering/unregistering sync databases, searching for packages, and managing database lists. (db_test.go)
• Introduced new tests in deps_test.go to validate dependency resolution using FindSatisfier for both database lists and package lists. (deps_test.go)