Internal chromedp runtime

This directory carries the runtime sources and embedded JavaScript from chromedp v0.16.0 (commit 7963c203ed5458147d27dc39a5c06d2b12e81664). The upstream license is retained in LICENSE. The upstream module checksum is h1:rOO4deOm4CbZgBCa8mD9g2rDyIoNs0BkgvNrlbp5ouk=.

Local changes, all to be re-applied when updating the copy:

• Import paths are rewritten from github.com/chromedp/chromedp to github.com/tmc/cdp/internal/chromedp.
• chromedp.go adds WithExistingTarget: canceling a borrowed attachment releases its session without closing the browser’s target. WithTargetID and newly allocated targets retain their existing close-on-cancel behavior. Invalid borrowed-target options, including conflicting target options and a browser-context option on a borrowed target, fail during Run, before allocation.
• chromedp.go moves the “can not be used before Browser is initialized” panics of WithNewBrowserContext and WithExistingBrowserContext from the options into NewContext, after option collection, so they apply in either option order.
• chromedp.go makes a failed browser allocation sticky: Run records the error and returns it on later calls instead of allocating again, which would close the allocator’s one-shot channel twice and panic.
• The //go:generate go run gen.go directives are removed from kb/kb.go, device/device.go, and the templates in kb/gen.go and device/gen.go, so go generate ./... does not regenerate those files from live sources and drift from the pinned version. Run gen.go by hand only as part of an update.

The MCP/browser implementation imports this package. The public cdpscripttest package and its CLI still use upstream chromedp, preserving their exported allocator options and action types. Contexts, options and concrete runtime types from the two implementations must not be exchanged. Protocol data types remain provided by the shared cdproto dependency. The shared browser feature list is a string, so each runtime can construct its own allocator option.

The runtime sources, kb, device, embedded js, and license are copied here; the upstream module file, test image fixtures, and upstream test suite are not. The local configuration and lifecycle regression tests cover the changed behavior. Changes to this copy require comparison with the pinned upstream source and review of the upstream tests affected by the update. Preserve source and license provenance when updating; do not edit the Go module cache.

An internal import path keeps versioned go install working without a module replacement directive. This is a maintained source copy, not an independently released module. Remove it when an upstream API can supply the required borrowed attachment contract, after qualifying the same lifecycle tests.