- Fix timestamp format to use ISO-8601 with Z timezone as required by API
- Rename handler class to TofuPilotLogHandler for clarity
- Improve code organization and comments
- Add examples of different log levels

Add missing procedure_id to testing_examples

This commit adds a new assembly test example that demonstrates how to
collect 100 voltage measurements over time using multi-dimensional
measurements. The voltage_sampling_test() function returns a list of
(timestamp, voltage) tuples that can be visualized and analyzed in
TofuPilot.

Key features:
- Samples 100 voltage measurements during test execution
- Returns multi-dimensional data as list of tuples
- Includes proper units for each dimension (time in seconds, voltage in V)
- Validates all samples against defined limits (10.0V - 12.0V)
- Integrated into the FVT4 assembly test procedure