python(feat): ULog data imports

[wei-qlu]

Summary

Adds PX4 ULog as a supported data import format in the Python client. ULog files are self-describing, so import is one call with no schema:

client.data_import.import_from_path("flight.ulg", asset=asset)

• Channels are detected client-side (the import service has no ULog detect endpoint) and mirror the backend importer, so a detected config imports unchanged. Detection reads only the file header and never decodes data records.
• detect_config returns every channel for inspection; drop, rename, or retype them before importing. relative_start_time (anchors the timeline; takes precedence over the log's GPS fix, required for logs without one), info_keys, param_keys, and parse_error_policy are all configurable.
• Requires the new optional ulog extra: pip install sift-stack-py[ulog].

Test

• Unit tests for the byte-level scanner, channel enumeration, type mapping, proto round-trip, and an end-to-end detect on a sample .ulg.
• Manual QA: .ulg file imports with confirmed channels, types, and timestamps.

[github-actions]

Python docs preview: https://sift-stack.github.io/sift/python/pr-663/

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