Cache action keys are declared with --input

cache action get and cache action put now accept repeatable --input specs (paths, path:, value:, env: variables, and stdin) so scripts declare their inputs directly instead of precomputing a hash. The standalone cache hash command and the --key option on cache blob are removed. cache action get --if-success only exits 0 when the cache has a hit and the recorded exit code was 0, so wrappers re-run on miss or cached failure.