CI: update modernize and auto-fix a few issues

[cce]

Summary

The go maintainers have deprecated the old paths for running modernize, and moved to a new location. In https://go.dev/issue/71859 they detail how this will end up in an official go fix command in 1.26.

This PR updates the Makefile to run the new modernize tool and flips our list of explicitly-enabled linters to an explicitly-disabled list, so new ones will show up as they are released.

Touching cmd/algofix/fix.go set off the "unused" linter, and fixing that revealed that huge chunks of algofix are unused (copy-pasted from an old version of the go fix tool), so this removes all that unused code.

Test Plan

Existing tests should pass.

Closes #6465.

[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
106384	2	106382	2481

View the top 2 failed test(s) by shortest run time

::TestMain

Stack Traces | 0s run time

FAIL	github..../test/e2e-go/restAPI [build failed]

::TestMain

Stack Traces | 0s run time

FAIL	github..../go-algorand/ledger/simulation [build failed]

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[gmalouf]

@cce some linter errors to work through

[Copilot]

Pull Request Overview

This PR updates the CI tooling to use the new location for the Go modernize tool and applies auto-fixes for code modernization. The changes include updating the Makefile to use the new modernize tool path and configuring which linters to run, while also removing large portions of unused code from the algofix tool that were copied from an older version of the go fix command.

Key changes:

• Updated Makefile to use new modernize tool location with explicit linter configuration
• Applied automated modernizations: replaced strings.Split with strings.SplitSeq, reflect.TypeOf with reflect.TypeFor, and context.WithCancel with t.Context()
• Removed ~800 lines of unused code from algofix including typecheck.go, import tests, and unused helper functions

Reviewed Changes

Copilot reviewed 35 out of 35 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Makefile	Updated modernize tool path and linter configuration
Multiple test files	Applied strings.SplitSeq and t.Context() modernizations
Multiple source files	Applied reflect.TypeFor modernization
cmd/algofix/*.go	Removed unused typecheck, import test code, and helper functions
cmd/algofix/deadlock_test.go	Replaced string(buf.Bytes()) with buf.String()

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[gmalouf]

This makes sense to me, enjoyed reading the story behind TypeFor on https://blog.carlana.net/post/2024/golang-reflect-type-for/.