Add CANMessage timestamp

[wsilverio]

This PR aims to add a microsecond timestamp support to isobus::CANMessage, propagated from the underlying CANMessageFrame.

Motivation:

Enables timing for latency analysis, diagnostics, and time-sensitive applications.

Based on #680

Semantics:

• Single-frame: timestamp of the originating CANMessageFrame, as reported by the hardware layer
• Multi-frame messages (RX only): timestamp of the last data-transfer frame
  • The last frame represents when the message becomes fully available to upper layers
  • Multi-frame TX is out of scope (would require new callback infrastructure)

Implementation:

• Added timestamp_us = 0 parameter to CANMessage constructors
• Added CANMessage::get_timestamp_us() getter
• Propagated frame.timestamp_us via CANNetworkManager
• Forwarded timestamps in:
  • TransportProtocolManager
  • ExtendedTransportProtocolManager
  • FastPacketProtocol

Unit tests:

New and updated unit tests in the existing test files:

./<build>/test/unit_tests --gtest_filter="CAN_MESSAGE_TESTS.*:TransportProtocolTest.BroadcastMessageReceiving"

Note: some unrelated tests are currently failing on main. These failures are reproducible without this PR and were excluded to isolate the changes introduced here.
./<build>/test/unit_tests --gtest_filter=-VirtualTerminalTest.FullPoolAutoscalingWithVector:VirtualTerminalTest.FullPoolAutoscalingWithDataChunkCallbacks:VirtualTerminalTest.FullPoolAutoscalingWithPointer