v2.0.0

• Breaking: signed header values, session tokens, and credential scope
  components must now contain only printable ASCII characters.
• Breaking: per-request init.signing overrides now read only own properties,
  and string URLs must include a non-empty host.
• Changed: signed requests that materialize non-string bodies may return a
  stable Uint8Array, accept-encoding is excluded from default signing, and
  the public cache type now matches the runtime Map-like contract.
• Fixed SigV4Client recovery after transient secret hash digest failures,
  one-shot header retry preparation, and oversized retry delay handling.
• Documented stricter signing contracts, query plus-sign behavior, cache and
  credential lifetime, Host replacement, and clock-skew limits.
• Added selected AWS SigV4 testsuite vectors and S3-compatible integration
  coverage for reserved object-key characters.
• Refactored source and unit tests into focused modules while keeping the
  published package as a single-file dist entry.