[v1.0] Workspace restructuring & feature-gated optional dependencies

[jbrodovsky]

Description

Restructure workspace crates (core, sim, geonav) to prepare for unified v1.0 releases:

• Feature-gate heavy dependencies in strapdown-core (hdf5, netcdf, mcap, wmm) behind cargo features (features = ["hdf5"] etc.) for fast compilation of the minimal core library.
• Keep sim and geonav in the workspace, configuring dependencies and feature flags cleanly.
• Ensure all crates build cleanly with default features (minimal) and --all-features (full).
• Reaffirm 100% open-source licensing (MIT) across all components without paywalls or tiered gates.

Acceptance Criteria

• cargo build --workspace --no-default-features and cargo build --workspace --all-features both compile cleanly.
• All crates ready for v1.0 versioning.