[consensus] Benchmark application-controlled handoffs

[BrendanChou]

Builds Alto against commonwarexyz/monorepo#4739 and adds three application-controlled handoff modes:

• wait for parent certification before building
• prepare a candidate but hold it until parent certification
• prepare and publish before parent certification

Global stable-leader deployments cycle validators across the three modes with one-view terms. The dashboard records notarization and finalization latency from view entry alongside handoff lifecycle counters.

This is a draft while the upstream API is under review.

Validation:

• cargo test -p alto-chain --lib
• cargo test -p alto-deploy
• 50-validator deployment across 10 AWS regions

[cloudflare-workers-and-pages]

Deploying alto with    Cloudflare Pages

Latest commit:	7cd385f
Status:	✅  Deploy successful!
Preview URL:	https://f3db06ed.alto-8k4.pages.dev
Branch Preview URL:	https://bc-handoff-cohort-bench-v2.alto-8k4.pages.dev

View logs

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.36364% with 32 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.44%. Comparing base (1d87569) to head (7cd385f).

Files with missing lines	Patch %	Lines
deploy/src/main.rs	92.85%	10 Missing ⚠️
validator/src/main.rs	0.00%	9 Missing ⚠️
types/src/wasm.rs	0.00%	8 Missing ⚠️
follower/src/archive.rs	66.66%	1 Missing ⚠️
follower/src/main.rs	0.00%	1 Missing ⚠️
indexer/src/main.rs	0.00%	1 Missing ⚠️
inspector/src/main.rs	0.00%	1 Missing ⚠️
inspector/src/utils.rs	0.00%	1 Missing ⚠️

@@            Coverage Diff             @@
##             main     #207      +/-   ##
==========================================
+ Coverage   78.95%   79.44%   +0.49%     
==========================================
  Files          31       31              
  Lines        7013     7181     +168     
==========================================
+ Hits         5537     5705     +168     
  Misses       1476     1476              

Files with missing lines	Coverage Δ
chain/src/application.rs	98.55% <100.00%> (+0.04%)	⬆️
chain/src/engine.rs	99.03% <100.00%> (+0.07%)	⬆️
chain/src/indexer/backfiller/consumer.rs	88.31% <100.00%> (+0.07%)	⬆️
chain/src/indexer/backfiller/state.rs	100.00% <ø> (ø)
chain/src/lib.rs	98.32% <100.00%> (+0.02%)	⬆️
client/src/consensus.rs	82.28% <100.00%> (-0.26%)	⬇️
follower/src/engine.rs	97.34% <100.00%> (ø)
follower/src/resolver.rs	91.72% <100.00%> (ø)
indexer/src/lib.rs	95.58% <100.00%> (ø)
types/src/block.rs	87.64% <ø> (ø)
... and 9 more

---

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