CI: some improvements for faster PR builds

[cce]

Summary

• Don't use verbose logging in test output (effectively reverts testing: Set gotestsum format to standard-verbose #3634) so easier to see failures
• Consolidate Go setup with version detection & module caching to a single reusable action
• Don't use the travis-ci gimme tool to download Go environment (just rely on setup-go action)
• Remove initial build job and workspace archiving + downloading by downstream jobs
  • Remove ~600MB workspace archive (took a few minutes on each end to upload and download)
  • Start the downstream jobs right away without waiting for build
• Don't call apt update & install if we already have sqlite3 installed (saves ~1 minute) and don't need expect
• Skip apt trigger for man-db rebuild (saves 1-2 minutes) using fix from Disable man-db dpkg trigger actions/runner-images#10977
• Consistent libsodium caching across jobs/workflows
• Remove legacy GOCACHE NFS workaround from Eric/use mule in jenkins #1072 (no longer necessary in current Go versions)
• Add build-e2e Makefile target for E2E tests to build only the binaries they need (with race detection except kmd).
  • integration and e2e_expect use race detection binaries, but e2e_subs hasn't been using them (and still doesn't, when I tried it there were timeouts, probably due to crypto getting slower with race detection)
• Set NO_BUILD to skip unnecessary extra binary installation by local_install.sh
• Split e2e_subs job into two shards (and verify the shards ran)
• Add reusable Slack action to make ci-pr.yml shorter
• Add report job that puts failed tests into check summary
• Add custom branch- and job-aware Go mod and build caching

Test Plan

PR tests finish about 2x faster now without build cache, >2x when build cache sharing is effective.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 44.33%. Comparing base (03d24da) to head (9bcffcf).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

❗ There is a different number of reports uploaded between BASE (03d24da) and HEAD (9bcffcf). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (03d24da)	HEAD (9bcffcf)
	4	3

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6397      +/-   ##
==========================================
- Coverage   50.69%   44.33%   -6.37%     
==========================================
  Files         661      654       -7     
  Lines      110771   110683      -88     
==========================================
- Hits        56152    49067    -7085     
- Misses      51751    58549    +6798     
- Partials     2868     3067     +199     

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[Copilot]

Pull Request Overview

This PR implements multiple CI/CD improvements to significantly reduce PR build times by consolidating Go setup, eliminating workspace archiving, optimizing dependencies, and improving test parallelization.

• Removes the build job and workspace archiving/downloading (saves ~600MB transfers per job)
• Consolidates Go setup with version detection and module caching into reusable actions
• Adds new build-e2e Makefile target for optimized E2E test binary building
• Splits e2e_subs job into two shards and adds comprehensive test result reporting

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
.github/workflows/ci-pr.yml	Major restructuring removing build job, adding test sharding, using reusable actions
.github/workflows/ci-nightly.yml	Updates to use new reusable actions and consolidated Go setup
.github/actions/setup-go/action.yml	New reusable action for Go setup with advanced caching
.github/actions/setup-test/action.yml	New reusable action for test environment setup
.github/actions/slack-notify/action.yml	New reusable action for Slack notifications
Makefile	Adds build-e2e target, removes GOCACHE workaround, adds libsodium target
test/scripts/e2e.sh	Adds support for test suite sharding via E2E_SUBS_TESTSUITE
test/scripts/e2e_go_tests.sh	Updates to use new build-e2e target with NO_BUILD support
test/scripts/e2e_client_runner.py	Renames output file from results.json to testresults.json
scripts/travis/before_build.sh	Simplifies libsodium building using new Makefile target
scripts/travis/codegen_verification.sh	Removes gimme tool usage, uses standard make build
AGENTS.md	Updates filename and description for broader agent compatibility