fix: increase base ensureTimeout from 200ms to 400ms (backport #2849) (#2948)

## Summary

Increases the base `ensureTimeout` in consensus tests from 200ms to
400ms. This also raises `ensureProposalTimeout` (defined as
`ensureTimeout * 5`) from 1s to 2s. `ensureVoteTimeout` stays at 2s
(already adequate).

## Motivation

Celestia-core has more per-round work than upstream CometBFT:
- Propagation reactor
- CAT mempool
- App-driven timeouts

The 200ms base timeout was inherited from upstream, where it is also
known to be flaky
([cometbft#1923](cometbft/cometbft#1923)).
Upstream has not resolved their consensus test flakes. A modest increase
to 400ms better reflects the actual time consensus operations take in
celestia-core without meaningfully slowing down the test suite.

## Test plan
- [ ] `go test -v -run TestStateFullRound1 -count=10 ./consensus/`
passes
- [ ] CI passes on this PR

Refs: #2430 #1017 #2702

🤖 Generated with [Claude Code](https://claude.com/claude-code)<hr>This
is an automatic backport of pull request #2849 done by
[Mergify](https://mergify.com).
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Co-authored-by: Rootul P <rootulp@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

.changelog/unreleased/improvements/ci-consensus-test-timeouts.md

@@ -0,0 +1 @@
+Increase consensus test base ensureTimeout from 200ms to 400ms to reduce flaky test failures.

consensus/common_test.go

@@ -55,7 +55,7 @@ type cleanupFunc func()
 var (
 	config                *cfg.Config // NOTE: must be reset for each _test.go file
 	consensusReplayConfig *cfg.Config
-	ensureTimeout         = time.Millisecond * 200
+	ensureTimeout         = time.Millisecond * 400
 	ensureVoteTimeout     = time.Second * 2   // votes need longer timeout on slow CI with race detector
 	ensureProposalTimeout = ensureTimeout * 5 // proposals can be delayed by TimeoutCommit and scheduling jitter
 )