fix(common): preserve Error.cause in activity failures

[mohan-garimella]

What changed

• Preserve a native Error.cause when ensureApplicationFailure converts an Activity error.
• Add one focused common-package test covering conversion and serialization of the nested failure.

Why

Activity execution calls ensureApplicationFailure before the configured failure converter. The default converter already serializes TemporalFailure.cause, but the conversion step discarded the cause first. Libraries such as database clients commonly use Error.cause for the actionable underlying error, so Temporal history retained only the wrapper message.

This is intentionally narrower than #1734. It does not map AggregateError.errors, use ApplicationFailure.details, or change the failure protobuf.

Closes #2291

Verification

• pnpm -F @temporalio/proto run build
• pnpm -F @temporalio/common run build
• pnpm -F @temporalio/common run test — 39 passed
• Prettier check on changed files
• ESLint on changed files

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Guard serialization against cyclic error causes

When an Activity throws an Error whose cause graph is cyclic (for example, error.cause = error, which is permitted because cause is mutable), retaining that cause makes DefaultFailureConverter.errorToFailureInner recurse indefinitely through optionalErrorToOptionalFailure. Instead of returning an Activity failure, the worker hits a RangeError while encoding it; detect cycles before attaching or serializing the cause.

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