apollo_batcher: use finish proposal api

[itamar-starkware]

TL;DR

Removed deprecated SendProposalContent::Finish variant and migrated all callers to use the dedicated finish_proposal method.

What changed?

• Removed the SendProposalContent::Finish variant from the enum, leaving only SendProposalContent::Txs
• Removed the corresponding ProposalStatus::Finished variant from proposal status responses
• Eliminated the deprecated code path in Batcher::send_proposal_content that handled finish requests
• Updated all test cases and production code to use finish_proposal method with FinishProposalInput instead of sending finish content through send_proposal_content
• Updated comment references from SendProposalContent::Finish/Abort to proposal finalization/abort

How to test?

Run the existing test suite to verify that:

• All proposal validation flows work correctly with the new finish proposal method
• Error handling for invalid proposals still functions properly
• Concurrent proposal scenarios continue to work as expected

Why make this change?

This removes technical debt by eliminating a deprecated API pattern. The change consolidates proposal finishing into a dedicated method rather than overloading the content sending mechanism, resulting in cleaner separation of concerns and a more maintainable codebase.

---

Note

Medium Risk
Moderate risk because it changes a cross-crate API and response types between consensus and batcher; regressions would show up as proposals not finalizing or incorrect status handling, though changes are narrow and covered by updated tests.

Overview
Migrates proposal finalization off the overloaded send_proposal_content path by removing the deprecated SendProposalContent::Finish + ProposalStatus::Finished variants and routing all finish semantics through the dedicated finish_proposal(FinishProposalInput) -> FinishProposalStatus API.

Updates batcher logic, consensus-orchestrator validation flow (validate_proposal), and related mocks/tests to use finish_proposal, and adjusts docs/comments to refer to proposal finalization/abort rather than the old Finish/Abort stream semantics.

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[reviewable-StarkWare]

This change is 

[itamar-starkware]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• apollo_batcher: use send_txs_request and remove send_proposal_content #12976
• apollo_batcher: add send_txs_for_proposal api #12975
• apollo_batcher: use finish proposal api #12972 👈 (View in Graphite)
• apollo_batcher: add finish_proposal api #12952
• apollo_batcher: use abort_proposal api #12949
• apollo_batcher: add abort_proposal api #12945
• main

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[ArniStarkware]

@ArniStarkware reviewed 1 file.
Reviewable status: 1 of 7 files reviewed, all discussions resolved (waiting on TzahiTaub).

[ArniStarkware]

@ArniStarkware reviewed 6 files and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on TzahiTaub).

[ArniStarkware]

@ArniStarkware reviewed 7 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on TzahiTaub).

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