[Go Migration] Implement STEPPER_BUZZ command

[AndySze]

Problem

The STEPPER_BUZZ G-code command is not implemented in Go, causing test failures in manual_stepper.test and potentially other tests.

G-code:

STEPPER_BUZZ STEPPER=stepper_x

Expected behavior:

• Briefly moves the specified stepper motor back and forth
• Used for testing stepper configuration and wiring

Current Status

The command is not recognized or produces no output in Go.

Proposed Fix

Implement STEPPER_BUZZ command handler in Go that:

1. Accepts STEPPER=<name> parameter
2. Generates a brief move sequence (typically ±1mm)
3. Matches Python's output exactly

Reference Python implementation:
klippy/extras/force_move.py - cmd_STEPPER_BUZZ()

Files to modify:

• go/pkg/hosth4/gcode_handlers.go - Add STEPPER_BUZZ handler
• go/pkg/hosth4/runtime.go - Register command

Affected Tests

• manual_stepper.test
• Any test using STEPPER_BUZZ command

Verification

./scripts/go_migration_golden.py compare --only manual_stepper --mode strict

Parent Issue

Part of #1