added some missing message types

[joe-saronic]

Adds support for some message types I am messing with for possible state estimation use:

• SatVisibility: predicted sat positions
• ChannelStatus: actual sats positions
• BaseVectorGeod: same as *Cart, but in LLA
• DiskStatus: random diagnostic
• RxMessage: random diagnostic
• XPPSOffset: timing insights
• ReceiverTime: timing insights
• EndOfAtt: framing
• EndOfPVT: framing
• Comment

Only XPPSOffset is not found in the mega message dump: everything else is tested.

This PR introduces some other small changes:

1. Sub-block infrastructure for nested is formalized a bit (so we can add stuff like OutputLink much more simply later). This also allows round-tripping nested arrays, which was not a thing before
2. Makes a couple of types binrw instead of just br. This makes everything correctly round-trippable. Only types present in the mega dump are tested. This uses the same approach as chore: fix fuzzing #50 (which is why I felt free to add it here), with the addition of the relatively transparent nested block handling.
3. Fixes a couple of minor clippy issues.

[Copilot]

Pull request overview

This PR expands libsbf’s SBF parsing/writing coverage by adding several additional message/block types and by formalizing nested/sub-block handling so more block families can be round-tripped using binrw.

Changes:

• Added parsing support for additional message kinds (e.g., SatVisibility, ChannelStatus, BaseVectorGeod, DiskStatus, RxMessage, ReceiverTime, EndOfAtt, EndOfPVT, Comment, XPPSOffset).
• Introduced SubBlock/NestedBlock infrastructure to correctly pad and round-trip nested and fixed-length sub-block arrays.
• Converted many existing message structs from BinRead-only to #[binrw] + explicit #[bw(map=...)] so sentinel-based Option fields serialize back to SBF.

Reviewed changes

Copilot reviewed 33 out of 33 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
Cargo.toml	Bumps crate version to 0.16.0.
src/lib.rs	Adds SubBlock/NestedBlock infrastructure and registers new message kinds.
src/parser.rs	Adds parsing branches for newly supported message kinds (stream + datagram).
src/reader.rs	Minor doc/test cleanup.
src/mega_test.rs	Extends mega-file tests for new message kinds + roundtrip harness.
src/messages/mod.rs	Exposes new message modules and re-exports new types.
src/messages/att_cov_euler.rs	(Not changed in provided diff).
src/messages/aux_ant_positions.rs	Moves to #[binrw] and uses SubBlock for padded sub-block arrays.
src/messages/base_vector_cart.rs	Moves to #[binrw] and uses SubBlock for vector sub-block arrays.
src/messages/base_vector_geod.rs	New: BaseVectorGeod block support (LLA/ENU baseline).
src/messages/bds_ion.rs	(Not changed in provided diff).
src/messages/channel_status.rs	New: ChannelStatus with nested sub-block structure.
src/messages/comment.rs	New: Comment block.
src/messages/disk_status.rs	New: DiskStatus and DiskData sub-block.
src/messages/end_of_att.rs	New: EndOfAtt framing block.
src/messages/end_of_pvt.rs	New: EndOfPVT framing block.
src/messages/ext_event.rs	Moves to #[binrw] + #[bw(map=...)] for sentinel options.
src/messages/ext_event_ins_nav_cart.rs	Moves to #[binrw] + #[bw(map=...)] for sentinel options.
src/messages/ext_event_ins_nav_geod.rs	Moves to #[binrw] + #[bw(map=...)] for sentinel options.
src/messages/ext_sensor_meas.rs	Uses SubBlock for padded sub-block arrays + adds missing #[bw(map=...)].
src/messages/ins_nav_cart.rs	Moves to #[binrw] + #[bw(map=...)] for sentinel options.
src/messages/ins_nav_geod.rs	Moves to #[binrw] + #[bw(map=...)] for sentinel options.
src/messages/meas_epoch.rs	Formalizes nested sub-block parsing/writing via NestedBlock.
src/messages/meas_extra.rs	Uses SubBlock for padded sub-block arrays and removes per-item align padding.
src/messages/nav_cart.rs	Moves to #[binrw] + #[bw(map=...)] for sentinel options.
src/messages/pos_cart.rs	Moves to #[binrw] + #[bw(map=...)] for sentinel options.
src/messages/pvt_cartesian.rs	Moves to #[binrw] + #[bw(map=...)] for sentinel options.
src/messages/pvt_geodetic.rs	Moves to #[binrw], adds Datum/PvtError write conversions, and sentinel #[bw(map=...)].
src/messages/quality_ind.rs	Adds QualityIndicator -> u16 encoding and round-trip support.
src/messages/receiver_status.rs	Moves to #[binrw] and uses SubBlock for padded sub-block arrays.
src/messages/receiver_time.rs	New: ReceiverTime timing block.
src/messages/rf_status.rs	Moves to #[binrw] and uses SubBlock for padded sub-block arrays.
src/messages/rx_message.rs	New: RxMessage diagnostic block.
src/messages/sat_visibility.rs	New: SatVisibility and SatInfo sub-block.
src/messages/x_pps_offset.rs	New: XPPSOffset timing block.

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