# why
`page.snapshot()` had no timeout param, nor did some of its internal
helpers. the helpers that it calls are also called by other functions in
the codebase that require timeout handling. this PR wires the `progress`
object through the shared downstream helpers, and also exposes a user
facing `timeout` param in `page.snapshot()`

# what changed
- added a snapshot timeout in milliseconds to typescript, python, & go.
omission or `0` keeps snapshots unlimited.
- made one deadline cover frame readiness, element lookup, document &
accessibility tree reads, & frame traversal
- allowed internal snapshot calls to reuse a caller's remaining time &
timeout error instead of starting a new budget.
- stopped retries, fallback reads, & further frame traversal after
expiry. temporary element references are released, including those
returned after timeout. already-issued browser commands can still
finish.
- updated sdk response waits to allow the requested timeout plus
delivery grace, with no response deadline for unlimited snapshots

# test plan
- `capture.test.ts` checks public & inherited deadlines, unlimited
snapshots, expiry preventing further reads or fallback, & cleanup of
ignored elements.
- `domTree.test.ts` & `a11yTree.test.ts` check that expired reads cannot
retry or fall back, including when the deadline timer has not fired yet.
- `focusSelectors.test.ts` checks that both selector lookup paths
release element references returned after timeout. focused accessibility
tests also check reference cleanup after successful reads.
- protocol & sdk tests cover omitted, zero, positive, & invalid
timeouts, option forwarding in all three sdks, & response waits. the
typescript package test checks that the published snapshot options
include the new field.

<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Adds an optional `timeout` param to `page.snapshot()` so callers can
bound the entire snapshot operation. Omitted timeouts now default to 20
seconds instead of running unlimited.

- Exposes `timeout` in the TypeScript, Python, and Go SDKs; passing `0`
keeps snapshots unlimited.
- Uses one deadline for frame readiness, element lookup,
DOM/accessibility tree reads, and frame traversal, and lets snapshots
reuse the caller's remaining time instead of starting a new budget.
- Stops retries, fallback reads (including focus-scope and
ignore-locator fallback), and further frame traversal after expiry,
releasing temporary element references even when they return after the
timeout.
- SDK response waits now add delivery grace to the requested timeout and
skip the deadline entirely for unlimited snapshots.

<sup>Written for commit 4054cdbb64468fa93b7a7d27152ad07bc3accaa7.
Summary will update on new commits.</sup>

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