[MAINT]: Introduce stricter linter rules for new code

[deiga]

Before the change?

• New code and existing code forced to use same linter rules

After the change?

• Enables holding new code to a stricter standard
• Adds make lintcheck-new to run stricter linters on only code since HEAD of main
• Adds make lintcheck-strict to run stricter linters on whole codebase
  • Useful to see if some strict linters can be moved to default config
• Refactor ci.yaml workflow, to run linters in parallel using golangci-lint-action
  • This enables inline linter complaints in PRs

Pull request checklist

• Schema migrations have been created if needed (example)
• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

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[github-actions]

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[Copilot]

Pull request overview

This PR separates baseline linting from stricter linting so new code can be held to higher standards without first fixing the entire existing codebase.

Changes:

• Adds a strict golangci-lint overlay enabling forcetypeassert.
• Adds Makefile targets for merged strict config generation and strict/new lint checks.
• Splits CI linting into dedicated parallel jobs using golangci-lint-action.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 6 comments.

File	Description
GNUmakefile	Adds generated merged lint config target plus strict/new lint targets.
.golangci.strict.yml	Defines stricter lint rules for new code.
.gitignore	Ignores the generated merged golangci-lint config.
.github/workflows/ci.yaml	Moves linting into separate CI jobs and updates aggregate checks.

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[stevehipwell]

LGTM

[Copilot]

Pull request overview

Copilot reviewed 3 out of 4 changed files in this pull request and generated 5 comments.

[deiga]

@stevehipwell addressed Copilot comments

@robert-crandall could you please review this PR? :)