CI: enable error-handling linters and fix a few bugs

[cce]

Summary

While upgrading to golangci-lint v2.6.0 after #6474 and #6473, I enabled some more safety linters (not style linters) to see if anything turned up, and found these error-handling bugs spotted by the govet liter's nilness check, the nilnesserr linter, and the testifylint linter's error-is-as check.

Test Plan

Existing tests should pass.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.29%. Comparing base (495da8c) to head (9aaa7f6).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
network/p2pNetwork.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6479      +/-   ##
==========================================
- Coverage   47.44%   47.29%   -0.16%     
==========================================
  Files         666      659       -7     
  Lines       88310    88225      -85     
==========================================
- Hits        41900    41726     -174     
- Misses      43649    43733      +84     
- Partials     2761     2766       +5     

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[cce]

I just went through and ran golangci-lint run --enable-only govet --config .golangci.yml --new-from-rev="" to get the nilness errors in the whole codebase, and fixed those too. nilnesserr came up clean. testifylint error-is-as found another spot where the type was not correctly being asserted.

[algorandskiy]

LGTM except the local.go changes

[Copilot]

Pull Request Overview

This PR upgrades golangci-lint to v2.6.0 and enables several error-handling focused linters (nilness, nilnesserr, and testifylint's error-is-as check) to improve code safety. The changes fix multiple error-handling bugs discovered by these linters across the codebase.

Key changes:

• Fixes incorrect error variable usage in error handling and logging
• Replaces incorrect assertion methods with proper error-checking assertions
• Removes unreachable or incorrectly conditioned error-handling code

Reviewed Changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
.golangci.yml	Enables new linters (nilness, nilnesserr, testifylint) for improved error handling checks
.github/workflows/reviewdog.yml	Updates golangci-lint version to v2.6.0
scripts/buildtools/versions	Updates golangci-lint dependency version to v2.6.0
network/p2pNetwork.go	Fixes error variable mismatch in logging statement
test/netperf-go/puppeteer/puppeteer.go	Restructures error handling to properly check and handle errors from metric operations
test/e2e-go/features/participation/overlappingParticipationKeys_test.go	Removes unreachable error handling code
test/e2e-go/features/catchup/catchpointCatchup_test.go	Removes redundant nil check and fixes error message formatting
netdeploy/remote/nodecfg/nodeConfigurator.go	Removes unreachable error handling code
ledger/catchupaccessor.go	Fixes const declaration syntax (moved outside closing paren)
cmd/algorelay/relayCmd.go	Removes unreachable error handling code
cmd/dispenser/server.go	Fixes incorrect error usage in HTTP response
cmd/tealdbg/local.go	Removes unnecessary nil checks before logging errors
util/db/dbutil_test.go	Replaces require.Error with require.ErrorIs for proper error comparison
ledger/txtail_test.go	Replaces require.Truef(errors.As) with require.ErrorAsf
ledger/store/trackerdb/sqlitedriver/sql_test.go	Replaces require.False(errors.As) with require.NotErrorAs
ledger/ledger_test.go	Replaces require.True(errors.As) with require.ErrorAs and fixes error variable check
ledger/eval/prefetcher/prefetcher_test.go	Replaces require.True(errors.Is) with require.ErrorIs
data/txHandler_test.go	Replaces require.Error with require.ErrorIs for proper error comparison
daemon/algod/api/server/common/test/handlers_test.go	Changes error assertion from comparing error objects to comparing error strings
crypto/merklesignature/merkleSignatureScheme_test.go	Removes duplicate error assertion
catchup/universalFetcher_test.go	Fixes incorrect require.Error usage to properly check error type
agreement/pseudonode_test.go	Replaces require.ErrorAs with require.ErrorIs for proper error comparison
agreement/fuzzer/networkFacade_test.go	Replaces panic(nil) with descriptive panic message
test/linttest/lintissues.go	Removes test file for linter validation

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