fix: track press-and-hold per device action and make it thread-safe

[ndorin]

Summary

Fixes #1489.

• PressAndHoldHandler keyed holds by device only, in an unlocked static dictionary. Two holds on one device at once (e.g. cameraLeft + cameraUp for a diagonal PTZ move) collided: a duplicate-key exception, a second action that never started, and an axis that stopped about 1 s late.
• Holds are now keyed by device and action path via a new HandlePressAndHold(deviceKey, actionPath, content, action) overload. All 47 call sites pass their own path, and CameraControlMessenger keys its holds per action too.
• Start, heartbeat reset, release and timeout run under one lock, so each action starts once and stops once, in order. A timeout only stops its action if that hold is still current.
• The original device-only overload is kept for plugins that call it.

Not in this PR: SIMPLCameraMessenger, SIMPLVtcMessenger, IHasCodecCamerasMessenger and MobileControlSIMPLRoomBridge call GetPressAndHoldHandler with the message value (pressed/held/released) as the hold key, so heartbeats and releases never find the hold. That's a separate bug in those callers.

Test plan

• Messengers and MobileControl projects build.
• Harness against the real class: cameraLeft/cameraUp pressed at the same moment from two threads, held, released, 200 runs: each axis started and stopped exactly once every time.
• Release stops immediately; a hold with no heartbeat times out once; a late release after timeout does nothing; the device-only overload behaves as before.
• Diagonal PTZ on a real camera through Mobile Control.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟡 Changes recommended

Timer-generation races, failed-start cleanup, and global callback serialization remain unresolved.

Review effort: Balanced
Findings: 3

Open (3)

• Failed start callback leaves a permanently stuck action entry · New
• Global lock serializes device callbacks across unrelated actions · New
• Stale timer callbacks can stop a hold after a heartbeat · New

What changed in this PR

Fixes #1489 by tracking press-and-hold state per device action and synchronizing timer access.

Changes:

• Adds action-specific hold keys across 47 call sites.
• Synchronizes hold lifecycle operations.
• Preserves the legacy device-only overload.

File	Description
MobileControlEssentialsRoomBridge.cs	Keys master-volume holds per direction.
PressAndHoldHandler.cs	Adds action keys and synchronized timer management.
ILevelControlsMessenger.cs	Separates level-control holds.
IBasicVolumeControlsMessenger.cs	Separates volume holds.
CameraControlMessenger.cs	Separates PTZ holds per action.
ITransportMessenger.cs	Adds transport action keys.
ISetTopBoxControlsMessenger.cs	Adds set-top-box action keys.
INumericMessenger.cs	Adds numeric-button action keys.
IDvrMessenger.cs	Adds DVR action keys.
IDPadMessenger.cs	Adds directional-pad action keys.
IColorMessenger.cs	Adds color-button action keys.
IChannelMessenger.cs	Adds channel-control action keys.

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