Migrate CI to centralized SciML reusable workflows

[ChrisRackauckas-Claude]

Please ignore until reviewed by @ChrisRackauckas

This PR normalizes the CI of LineSearch.jl to the SciML centralized reusable workflows in SciML/.github (every caller pinned @v1, secrets: inherit). Existing behavior and test matrices are preserved exactly.

Workflows converted

• Tests.yml -> matrix of tests.yml@v1 callers. Preserves the exact matrix: version ∈ {1, lts} × group ∈ {Core, LineSearchesJL, QA}, excluding QA on lts. Coverage stays on (caller default). The non-standard Enzyme Tests job (separate test/enzyme environment, custom Pkg.develop/instantiate + test/enzyme/runtests.jl) is kept as a regular step-based job in the same file since the reusable tests workflow cannot reproduce it.
• Documentation.yml -> documentation.yml@v1 caller with debug-documenter: true (original set JULIA_DEBUG=Documenter). Coverage stays on (caller default, matching original --code-coverage=user).
• Downgrade.yml -> downgrade.yml@v1 caller. Kept disabled (if: false, as in the original), preserving julia-version: "1.10", skip: "Pkg,TOML", allow-reresolve: false.
• FormatCheck.yml -> runic.yml@v1 caller.
• SpellCheck.yml -> spellcheck.yml@v1 caller.

Runic

The repo already ran Runic (via fredrikekre/runic-action). I ran Runic.main(["--check", "."]) (Runic v1.7.0) locally and it passed with no changes, so no formatting commit was needed.

Spellcheck / typos

Ran typos locally — no typos found, no _typos.toml needed.

Dependabot / CompatHelper

• No CompatHelper.yml existed, so nothing to remove.
• dependabot.yml: removed the crate-ci/typos ignore block (standing policy: keep everything current). Preserved the existing julia directories (/, /docs, /test) and added /test/enzyme (it has its own Project.toml). The github-actions block (directory: "/", weekly) and the julia block (daily, all-julia-packages group) are otherwise unchanged.
• TagBot.yml left unchanged.

Heads-up

• Branch protection / required status checks must be updated. The job/check names change under the reusable workflows (e.g. tests now report as Tests / Tests rather than Core - Julia 1), so any required-status-check names in branch protection need updating to match.
• Minor behavior diff: the original Documentation workflow used fail_ci_if_error: true on codecov; the centralized documentation.yml@v1 does not set that flag (defaults to false). This makes the docs build slightly more tolerant of codecov upload failures.

🤖 Generated with Claude Code