Release @wdio/devtools-backend 1.10.0 so the pinned npx path exists #305

Part of #277

BACKEND_NPM_VERSION = "1.10.0" in the adapter's constants.py is the version link for the published path, tier 4 of launch_or_attach(): npx @wdio/devtools-backend@<pinned>. That version does not exist on npm yet. The latest published is 1.9.1, and no published version carries the devtools-backend bin, so npx fails with "could not determine executable to run".

The changeset in #246 declares "@wdio/devtools-backend": minor, which takes 1.9.1 to 1.10.0 on the next release. So this ticket is just: cut that release, then verify the pinned path end to end.

Acceptance criteria

@wdio/devtools-backend@1.10.0 is on npm and its tarball contains an executable dist/server.js exposed as the devtools-backend bin. In a directory with no monorepo checkout, npx @wdio/devtools-backend@1.10.0 starts the dashboard and prints its listening line. A pip-installed adapter with no environment variables set reaches that path and captures a run. Consider #296 in the same pass, since the tarball currently ships src/ and tests/.

Size: S. Release blocker: must land before any PyPI publish. Depends on #246 being merged and released.