chore: migrate to oxlint, oxfmt and TypeScript 7

[chybisov]

Which Linear task is linked to this PR?

Part of EXBE-617

Why was it implemented this way?

Replaces ESLint + Prettier with oxlint + oxfmt (the jumper-frontend setup, without the React/Next parts) and moves to TypeScript 7. typescript-eslint does not run on TypeScript 7, so both changes go together.

• oxlint: typescript-eslint recommended rules + the four existing custom rules, plus oxlint's default correctness category (bug-catching rules such as no-debugger, no-cond-assign, no-loss-of-precision; it finds nothing in the current code). CI and the pre-commit hook fail on warnings. The two public any types in src/api.ts keep their type and get a disable comment.
• scripts/prepublishOnly.js refuses to publish when the build output (entry points and the _cjs/_esm type markers) is missing.
• CI hardening: the pnpm store cache is off unless a read-only job opts in; tests.yaml does not persist the checkout token. LICENSE.md stays verbatim (oxfmt ignores it). VS Code turns on the TypeScript 7 extension (js/ts.experimental.useTsgo).
• oxfmt: the existing Prettier options; src/ has zero format changes. A separate style: commit formats a few non-source files once.
• TypeScript 7.0: no tsconfig change needed. The .d.ts output only changes the quote style inside as const tuple types; the .js output is byte-identical.
• pnpm install no longer builds (prepare removed); the publish workflow, CI and pre-push still build.
• New tests.yaml runs lint, format check, typecheck and build on PRs.
• Removed the dead jest.config.js and the unused tsconfig.node.json.

Editor: install the "TypeScript 7" VS Code extension (TypeScriptTeam.native-preview, see README).

Note: git-branch installs ("@lifi/types": "github:lifinance/types#<branch>") no longer build the package (pnpm 10 already blocks them by default). Use a published prerelease instead (release-preview label after part 2).

Part 1 of 2. Part 2 moves releases to Changesets.

Checklist before requesting a review

• I have performed a self-review and testing of my code.
• This pull request is focused and addresses a single problem.