Remove unnecessary closure variable reassignments

[YoshihitoAso]

This pull request primarily removes unnecessary variable reassignments in range loops throughout the codebase, which were previously used to avoid closure capture issues in goroutines and subtests. These changes simplify the code and rely on Go's improved handling of range variable capture since Go 1.22.

Additionally, a new linter is enabled to help catch potential issues with loop variables in the future.

Linter configuration

• Enabled the copyloopvar linter in .golangci.yml to help detect incorrect usage of loop variables in closures.

Code cleanup and simplification

• Removed redundant reassignments of range variables (e.g., var := var) in test files and goroutine closures.

[Copilot]

Pull Request Overview

This pull request removes unnecessary variable reassignments in range loops that were previously used to avoid closure capture issues in goroutines and subtests. With Go 1.22's improved handling of range variable capture, these reassignments are no longer needed.

• Removes redundant var := var reassignments in test files and goroutine closures
• Enables the copyloopvar linter to catch potential loop variable issues
• Simplifies code by relying on Go's native range variable handling

Reviewed Changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
.golangci.yml	Enables the copyloopvar linter
tests/state_test.go	Removes subtest variable reassignment in range loop
rpc/client_test.go	Removes index variable reassignment in goroutine
p2p/peer.go	Removes proto variable reassignment in goroutine
p2p/nodestate/nodestate.go	Removes callback variable reassignment
p2p/discover/v5wire/encoding_test.go	Removes test variable reassignment in subtest
node/node_test.go	Removes test variable reassignment in subtest
node/api_test.go	Removes test variable reassignment in parallel subtest
les/commons.go	Removes version variable reassignment in protocol creation
les/api_test.go	Removes client variables reassignment in goroutine
eth/tracers/tracers_test.go	Removes file variable reassignment in parallel subtest
eth/protocols/snap/handler.go	Removes version variable reassignment
eth/protocols/eth/handler.go	Removes version variable reassignment
eth/handler_eth_test.go	Removes sink and channel variable reassignments in goroutines
eth/fetcher/block_fetcher.go	Removes hashes variable reassignment in goroutine
eth/downloader/downloader.go	Removes function variable reassignment in goroutine
cmd/geth/accountcmd_test.go	Removes test variable reassignment in parallel subtest
accounts/abi/unpack_test.go	Removes test case variable reassignment in subtest
accounts/abi/event_test.go	Removes test case variable reassignment in subtest

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