# why
`browser.close()` & `browser.context.close()` should both explicitly
terminate the browser

before this PR, `browser.close()` only terminated launched browsers when
`keepAlive` was false. keepalive browsers were disconnected, connected
local browsers did not receive `Browser.close`, & connected Browserbase
sessions were not released

`browser.context.close()` disposed worker state without terminating the
browser. this was semantically weird, because it was never really clear
what it was supposed to be "closing". it was not a full
`stagehand.close()`, nor was it a full `browser.close()`. this method is
being left in place so as to not break downstream callers, but it is now
just an alias for `browser.close()`

### after this PR:
- `browser.close()` & `browser.context.close()` invoke the same close
operation. `context.close` is also removed from the protocol
- explicit close terminates launched local browsers for either
`keepAlive` value;
- explicit close sends CDP `Browser.close` to connected local browsers;
- explicit close requests release of launched & connected Browserbase
sessions; &
- `keepAlive` only affects internal invalidation after initialization
failure, not explicit close

# what changed
- stopped calling public `browser.close()` when `Stagehand.create()`
fails; failed initialization now makes the SDK browser handle unusable &
applies the existing keepalive cleanup behavior
- changed ambiguous `Stagehand.create()` failure cleanup to invalidate
the browser without overriding its keepalive policy
- made explicit close invoke the local process termination callback for
both keepalive values
- added explicit Browserbase session release for launched & connected
sessions
- added root CDP `Browser.close` handling for connected local browsers
- kept the host CDP transport open until the provider-specific
termination request is dispatched
- continued cleanup after termination or transport errors & preserved
combined failures
- changed each public context wrapper to call its owning browser's
memoized close operation instead of sending `context.close`
- removed the unused `context.close` operation from the protocol,
extension, generated SDK models, & RPC timeout tables

# test plan
- [x] TypeScript, Python, & Go tests verify explicit close terminates
launched local browsers for both keepalive values.
- [x] TypeScript, Python, & Go tests verify connected local close sends
CDP `Browser.close`.
- [x] TypeScript, Python, & Go tests verify launched & connected
Browserbase close requests session release.
- [x] TypeScript, Python, & Go tests verify initialization failure uses
internal invalidation instead of explicit termination.
- [x] TypeScript, Python, & Go tests verify browser & context close
share one memoized operation.
- [x] TypeScript, Python, & Go tests verify context close no longer
sends the legacy `context.close` RPC.