feat: calculate expected live position for remote drivers

[AndyEveritt]

Calculate the expected live position using the phase stepping method to enable better live position feedback of remote drivers.

Without this the live machine position is only updated frequently during homing moves and once per segment, this allows the inter segment position to be calculated in a more efficient way than using interrupts for the remote drivers

[Copilot]

Pull request overview

This PR improves live position reporting for (especially remote) drivers by computing an expected position from the active motion segment (phase-stepping style evaluation), instead of only updating at segment boundaries.

Changes:

• Split “query motion” into a const/non-mutating GetCurrentMotion and a mutating UpdateCurrentMotion (advances segments as needed), for both Move and DriveMovement.
• Use the new const motion query in Move::GetLiveMachineCoordinates() to provide more frequent live coordinate updates.
• Improve step error debug output to include drive index and axis/extruder identifier; adjust segment preparation so u is available for the new motion evaluation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/Movement/Move.h	Makes GetCurrentMotion const and adds UpdateCurrentMotion API.
src/Movement/Move.cpp	Switches phase-stepping call sites to UpdateCurrentMotion; computes live coords via per-drive motion evaluation.
src/Movement/DriveMovement.h	Introduces const GetCurrentMotion (non-advancing) and UpdateCurrentMotion (advancing) with updated docs.
src/Movement/DriveMovement.cpp	Ensures u is calculated early; enhances step error logging context.

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