Add a short-lived cache for non-recoverable errors

[ysaito1001]

Motivation and Context

This PR follows #4774 in the series to support consistent credentials refresh across credential providers. It brings StaticStabilityCache in line with a later revision of the design, which protects a credentials source even in the event of non-recoverable errors.

• PR 1 — Add identity-cache invalidation #4766 (generic hooks)
• PR 2 — Add static stability cache #4774 (StaticStabilityCache + AWS-land signals)
• PR 2 follow-up (this PR) — a short-lived cache for non-recoverable errors (aws-runtime)
• PR 3 — aws-config + codegen (wiring)

These PRs merge into the ysaito/consistent-credentials-refresh feature branch.

Description

Non-recoverable refresh errors intentionally skip the refresh backoff so actionable errors (e.g. "reauthenticate") surface immediately. But that means an application that catches such an error and retries in a loop would call the credential source (e.g. STS) on every retry. To protect the source, the SDK must briefly cache the error and re-raise it to subsequent callers without re-contacting the source.

This PR adds a short-lived, jittered cache for non-recoverable errors to StaticStabilityCache, separate from the existing refresh backoff. It adds no public API and changes no client default behavior on its own.

Specifically, on a non-recoverable refresh failure, the cache stores the error with an expiry of now + uniform_random(1s..=5s) and still raises it to the current caller. While that window is live, subsequent resolutions re-raise the cached error without contacting the source — the gate is checked after acquiring the single-flight refresh lock, before any source call. A successful refresh clears the cached error.

Testing

• Re-vendored the modeled scenarios in aws-runtime/test-data/credential-refresh-tests.json to match the revised design
• Added manual tests for behaviors the sequential JSON runner cannot express:
  • mandatory_concurrent_non_recoverable_reuses_cached_error — concurrent callers on an expired credential: one performs the refresh and fails non-recoverably; the others reuse the cached error, so the source is contacted exactly once.
  • jittered_error_cache_bounds — the cache window always falls in 1..=5s, the invariant the
    deterministic suite relies on.

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• AWS SDK (ignoring whitespace)
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• No codegen difference in the Server Test Python
• No codegen difference in the Server Test Typescript

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