fix(task): fold appended CLI args into the input cache fingerprint
Address review feedback. The fingerprint hashed only the command string,
but the executed command is get_script_with_args(command, argv), so
`deno task build foo` and `deno task build bar` produced the same
fingerprint and the second run was wrongly skipped with the first run's
args. Add argv to the cache key, hash it (length-prefixed) into the
fingerprint, and render the cached-output line with the appended args so
it reflects what actually ran.
Expand the spec test to cover the argv case plus env-var invalidation,
command change, and the glob-matches-nothing bail-out. Document the
first-pass caveats (outputs not restored on hit; tasks that mutate their
own inputs never cache) on the cache module and the deno.json `files`
schema.
