fix(sdk): Harden auth cache key, validity, and file GC

[gtema]

• get_config_identity_hash: replace DefaultHasher with SHA-256 over a
  field-tagged canonical string. DefaultHasher is unstable across Rust
  releases (orphans cache files on a toolchain bump) and skipping None
  fields let differently-shaped identities collide on the same cache
  file, letting the wildcard scope matcher return another user's token
• change auth hash type u64 -> String throughout State/session/
  openstack_async to carry the new hash
• apply a 60s validity margin when selecting a cached token for use
  (get_scope_auth, find_scope_authz, find_valid_auth), keeping None for
  persistence-time filtering; avoids handing out a token that expires
  before the request completes
• deterministic scope priority (unscoped > project > domain > system)
  replacing HashMap-order-dependent token selection
• GC cache/lock files older than 7 days on first State::new() per
  process; gated with Once to avoid repeated directory scans when
  State::new() runs more than once per process
• fix unlocked first-read race: load_auth_state now creates the lock
  file if missing instead of skipping the lock silently
• prefix on-disk cache payload with a format-version byte so a schema
  change is logged distinctly from corruption
• drop Windows readonly attribute on cache files: it added no real
  confidentiality and broke the next write via NamedTempFile::persist/
  File::create

Signed-off-by: Artem Goncharov artem.goncharov@gmail.com