dev-qemu: Update HAL and use custom QEMU

[kurtjd]

This updates the qemu-riscv-hal dep so we get access to the new HAL which makes use of the new custom socket-backed virtual I2C controller/target and gpio.

Because this now requires a custom QEMU build, also added a script to pull our custom build from our odp-qemu-builder repo. Now, cargo run will automatically use that, and it is also used by CI/integration tests.

dev-qemu doesn't currently make use of the new HAL, this is just to get everything in place for folks to start using it to test and develop with.

Resolves #27

[Copilot]

Pull request overview

This PR updates the dev-qemu platform to use an updated QEMU HAL and switches execution to a custom ODP QEMU build (with the ec machine), fetched from GHCR and cached locally, so developers/CI can use socket-backed virtual I2C/GPIO going forward.

Changes:

• Add a unified qemu-ec.sh launcher that resolves a custom qemu-system-riscv32 from GHCR (or $QEMU) and is used as the Cargo runner.
• Update CI and integration-test flow to use the new runner and pre-warm the QEMU cache to avoid startup timeouts.
• Refresh dev-qemu docs and lockfile to reflect the updated HAL dependency set.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
scripts/integration-test.sh	Prepares (warms) the custom QEMU cache before launching dev-qemu in headless CI mode.
platform/dev-qemu/README.md	Documents the custom ec machine behavior, Docker/GHCR-based QEMU provisioning, sockets, and configuration knobs.
platform/dev-qemu/qemu-ec.sh	New single-source runner: pulls/caches custom QEMU and launches with ec machine + socket chardevs + defmt routing.
platform/dev-qemu/Cargo.lock	Updates embassy-qemu-riscv git rev and lockfile dependency graph for the new HAL.
platform/dev-qemu/.cargo/config.toml	Switches Cargo runner to ./qemu-ec.sh and simplifies the run-headless alias.
.github/workflows/check.yml	Updates integration-test job env/pkgs to align with GHCR-provided QEMU instead of apt-installed QEMU.