Cardano Updates

workflow_dispatch only (manual trigger). Runs on benchmark-new
with cardano-wallet-bench label. TMPDIR set to /tmp/gha-bench
to avoid permission conflicts with Buildkite's /tmp/bench.

Build docker image via nix, run mainnet and preview boot syncs.
Mithril full sync left out (was manual-triggered in Buildkite).

Move nix build, evaluate shell, and package build from Buildkite to GHA.
Package artifacts uploaded via actions/upload-artifact.

Move Check Nix (linux) and Dev Shell Attic Cache from Buildkite to GHA.
Attic cache push runs only on master pushes and requires ATTIC_TOKEN secret.

Move TODO List, HLS check, Cabal Build, and git-revision check
from Buildkite to GHA. Remove entire Code Quality group from Buildkite.

All tests use nix run instead of cabal test. Removes Linux unit test
steps from Buildkite pipeline (replaced by GHA self-hosted runners).

Move 6 code quality checks from Buildkite to GHA self-hosted runners:
Code Format, HLint, Cabal Configure, Bash Lint, EOL, Swagger validation.

Manual workflow_dispatch job that runs snapshot.sh + full sync
via Docker, mirroring the Buildkite block step.

Aggregates all benchmark results after they complete,
mirroring the Buildkite Benchmarks history step.