cmd: enable errcheck across cmd/* CLI tooling and fix violations

[Sahil-4555]

Continues the errcheck rollout for #22538 into ten cmd/* packages: cmd/capcli, cmd/caplin/caplin1, cmd/evm(+internal/t8ntool), cmd/integration/commands, cmd/rlpdump, cmd/rpcdaemon/cli, cmd/rpcdaemon/health, cmd/utils/app, cmd/utils/cmdtest.

Notable fixes beyond lint-satisfying:

• missingBlocks (import tooling) called headBlock.NumberU64() right after a discarded chainDB.View call - a failed view left headBlock nil, a live panic. Traced the surrounding branch to its original 2021 commit and confirmed it never actually differentiated behavior; removed the dead branch along with the now-unused blockReader parameter.
• A slot-range verification loop in capcli logged "Successfully checked" unconditionally even when ReadBlockBySlot failed mid-loop, defeating the point of a checking tool.
• t8ntool's DumpToCollector (the tool's actual output) and MakePreState's genesis-account setters were silently discarded; the latter now panics consistently with the rest of that function instead of a mix of checked/unchecked calls.
• caplin1.OpenCaplinDatabase's startup RemoveAll/MkdirAll/genesisDb.Initialize calls were unchecked, risking either a skipped wipeout or a MustOpen panic on a missing directory instead of a clear error.

Deduplicated the defer l.Unlock() datadir-flock pattern (copied ~15 times across snapshots_cmd.go/squeeze_cmd.go/backtest_commitment_cmd.go) into a single unlockDatadir helper, matching the convention already established in backtest_commitment_cmd.go rather than inventing a new one.

[Copilot]

Pull request overview

Enables errcheck across ten CLI packages and handles previously ignored errors.

Changes:

• Propagates database, state, output, and filesystem errors.
• Fixes import and snapshot-verification failure handling.
• Centralizes datadir unlock handling.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
.golangci.yml	Enables errcheck for migrated packages.
cmd/capcli/cli.go	Propagates snapshot and state errors.
cmd/caplin/caplin1/run.go	Checks database setup and initialization errors.
cmd/evm/internal/t8ntool/execution.go	Checks genesis state mutations.
cmd/evm/internal/t8ntool/transition.go	Handles dump and cleanup errors.
cmd/evm/runner.go	Handles state mutation and cleanup errors.
cmd/evm/staterunner.go	Reports temporary-directory cleanup failures.
cmd/integration/commands/commitment.go	Checks output synchronization.
cmd/integration/commands/stages.go	Explicitly handles intentional ignored errors.
cmd/integration/commands/state_history.go	Propagates history scan and unlock errors.
cmd/rlpdump/main.go	Propagates RLP list-finalization errors.
cmd/rpcdaemon/cli/config.go	Handles database-view and gRPC serving errors.
cmd/rpcdaemon/health/health.go	Reports response-write failures.
cmd/utils/app/backtest_commitment_cmd.go	Uses shared datadir unlock handling.
cmd/utils/app/import_cmd.go	Propagates database errors and simplifies missing-block detection.
cmd/utils/app/snapshots_cmd.go	Handles unlock and deletion errors.
cmd/utils/app/squeeze_cmd.go	Uses shared datadir unlock handling.
cmd/utils/cmdtest/test_cmd.go	Propagates stdin write errors and marks intentional ignores.

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[Copilot]

Pull request overview

Copilot reviewed 19 out of 19 changed files in this pull request and generated 1 comment.