test: expand mockgrbl motion integration coverage

[ianbruene]

Motivation

• Extend the Linux-only mockgrbl_e2e integration suite to cover multi-motion queuing and realtime reset behavior that were previously untested.

Description

• Add TestDDGoQueuedAbsoluteJogSequencingAgainstMock to internal/integration/mockgrbl/mockgrbl_e2e_test.go, which queues three absolute machine-coordinate jogs (X, Y, Z) via controller.JogTo and asserts the mock planner executes them to final (-1, -1, -1) using both mock /state and the controller snapshot.
• Add TestDDGoRealtimeResetDuringJogAgainstMock to the same test file, which starts a long absolute jog, waits for active motion, issues a realtime soft reset via controller.Action(grbl.ActionSoftReset), and asserts the mock returns to Idle with active/queued motion cleared and a sane materialized X position.
• Both tests reuse the existing mock harness, real serial transport, bounded polling helpers (waitForMockState, waitForControllerState, etc.), tolerances (posTol) for motion assertions, and avoid changing production code or CI workflows.

Testing

• Ran go test -tags 'serial mockgrbl_e2e' ./internal/integration/mockgrbl, which passed.
• Ran go test ./..., which passed.
• Ran go test -tags serial ./internal/transport ./internal/ports ./internal/app ./internal/grbl, which passed.

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Codex Task