test: run ESP32 programs in QEMU

[jakebailey]

I was working on Xtensa panic/recover, but noticed that CI doesn't seem to run emulation. Fix that, and a bug found that only happens on full images.

There has to be another _qemu.go file, but that is not different than other systems.

[deadprogram]

Looks good overall, thanks for working on this @jakebailey

Two small things that were pointed out in an automated code review:

1. device.AsmFull has no clobber support, so the writes to a2/a3 in qemuExit are undeclared
   clobbers. It's safe here only because the waiti loop follows and nothing after reads them.
   Worth a comment saying a2 = SYS_exit (1), a3 = exit code, and that the trailing loop is
   what makes the missing clobber list OK.

2. targets/esp32.json and targets/esp32s3.json still have their own qemu-system-xtensa
   emulator lines. Those lack -semihosting and don't set the qemu build tag, so now that CI
   has a working xtensa QEMU on PATH they're broken rather than just unused. Can they be
   dropped in favor of the new esp32-qemu target?

[Copilot]

Pull request overview

Adds ESP32 QEMU execution to CI and corrects full-image flash segment placement.

Changes:

• Adds a dedicated ESP32 QEMU target with semihosting exit support.
• Runs an ESP32 program under Espressif QEMU in Linux CI.
• Fixes DROM/IROM offsets in full ESP32 images.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
.github/workflows/linux.yml	Installs Espressif QEMU and dependencies.
builder/esp.go	Corrects full-image flash offsets.
main_test.go	Adds QEMU execution and output cleanup.
src/runtime/runtime_esp32.go	Moves hardware abort implementation.
src/runtime/runtime_esp32_abort.go	Provides hardware ESP32 abort behavior.
src/runtime/runtime_esp32_qemu.go	Adds semihosting termination.
src/runtime/runtime_esp32xx.go	Moves shared exit implementation.
src/runtime/runtime_esp32xx_exit.go	Provides non-QEMU exit behavior.
targets/esp32-qemu.json	Defines the QEMU target.
targets/esp32.json	Removes QEMU from the hardware target.
targets/esp32s3.json	Removes the incompatible emulator setting.

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