apollo_propeller: rename shards param to units in reconstruct_blocking

[sirandreww-starkware]

Note

Low Risk
Low risk: a pure parameter rename in MessageProcessor::reconstruct_blocking with no behavioral or data-flow changes.

Overview
Renames the reconstruct_blocking argument from shards to units in message_processor.rs to better match PropellerUnit terminology, updating the internal call to reconstruct_data_shards accordingly.

^{Reviewed by Cursor Bugbot for commit 70d99d3. Bugbot is set up for automated code reviews on this repo. Configure here.}

[reviewable-StarkWare]

This change is 

[guy-starkware]

@guy-starkware reviewed 1 file and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on noamsp-starkware and ShahakShama).

[cursor]

PR Summary

Low Risk
Purely a local variable rename with no logic changes, so regression risk is minimal.

Overview
Renames the reconstruct_blocking parameter from shards to units in message_processor.rs, updating the call into reconstruct_data_shards accordingly.

No functional behavior changes; this is a naming/clarity tweak to better reflect that the function operates on PropellerUnits.

^{Reviewed by Cursor Bugbot for commit d629c4b. Bugbot is set up for automated code reviews on this repo. Configure here.}