Add unit tests for chart_datum_node and sea_surface_estimator

[rolker]

Summary

chart_datum_node and sea_surface_estimator have no unit tests. Key logic that should be covered:

sea_surface_estimator

• Tide range rejection: inject chart_datum and chart_datum_mhhw TF frames, feed odometry with Z values inside and outside the plausible range, verify map_tide transform is published or suppressed accordingly
• Buffer duration: verify transform is not published until minimum_buffer_duration is met
• tide_estimate debug topic: verify it publishes even when the estimate is rejected

chart_datum_node

• Dual pipeline: verify both MLLW and MHHW offsets are computed and published as TF frames
• MHHW fallback: verify node works correctly when MHHW grids are unavailable (only MLLW published)
• Debug topics: verify mllw_offset and mhhw_offset Float64 topics are published with correct values

Context

These nodes were recently extended with MHHW support and tide range rejection (#15, PR #16). The s57_layer costmap plugin has good test coverage for its tide offset behavior, but the upstream nodes that feed it do not.

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Authored-By: Claude Code Agent
Model: Claude Opus 4.6