Centralize CI on SciML reusable workflows

[ChrisRackauckas-Claude]

Please ignore until reviewed by @ChrisRackauckas

Converts the remaining inline CI to the centralized SciML reusable workflows (@v1), so every check is a central caller with secrets: "inherit".

Converted (inline -> central)

• FormatCheck.yml (runic): inline fredrikekre/runic-action -> runic.yml@v1
• SpellCheck.yml (typos-check): inline crate-ci/typos@v1.18.0 -> spellcheck.yml@v1
• Downgrade.yml (downgrade): inline julia-downgrade-compat -> downgrade.yml@v1, preserving julia-version: "1.10" and skip: "Pkg,TOML"

Already central (left unchanged)

• Tests.yml -> tests.yml@v1 (matrix 1, lts, pre), already secrets: "inherit"
• Documentation.yml -> documentation.yml@v1, already secrets: "inherit"

Other changes

• dependabot.yml: removed the crate-ci/typos version-ignore (no longer pinned inline); github-actions (weekly, /) and julia (daily, all-julia-packages: ["*"] over /, /docs, /test) blocks preserved.

Not changed

• QA.yml: a custom Aqua/QA job (test/qa). There is no central QA caller, so it is left as-is.
• TagBot.yml: unchanged.
• No CompatHelper.yml present.

Notes

• Runic ran clean (no formatting changes); the repo already ran Runic inline.
• typos ran clean (0 fixes needed).
• Heads up: check names change (e.g. format-check / runic -> the central Runic Format Check job name, spellcheck/downgrade job names change). Branch-protection required-status-check names will need updating accordingly.

🤖 Generated with Claude Code