Convert clients/js-legacy to oxlint and oxfmt

[clankmaxxing-clod]

Replaces ESLint + Prettier with oxlint and oxfmt for the clients/js-legacy package, mirroring solana-program/token-group#115, solana-program/token-metadata#120, solana-program/libraries#200, and solana-program/memo#415.

Changes

• package.json: dropped eslint, prettier, @eslint/js, typescript-eslint, eslint-config-prettier, eslint-plugin-prettier, eslint-plugin-require-extensions, and @solana/prettier-config-solana; added oxlint and oxfmt. Scripts now run the Oxc tools:
  • lint → oxlint --max-warnings 0
  • lint:fix → oxlint --fix
  • format → oxfmt --check src test
  • format:fix → oxfmt --write src test
  • removed the "prettier" config key.
• .oxlintrc.json (new) mirrors the old ESLint config: correctness category as errors; consistent-type-imports enforced; ban-ts-comment / no-explicit-any / no-unused-vars / no-empty-object-type disabled; import/extensions (import plugin) replaces eslint-plugin-require-extensions and stays disabled for test/examples.
• .oxfmtrc.json (new) migrated from @solana/prettier-config-solana (printWidth 120, tabWidth 4, single quotes, semicolons, arrowParens: avoid).
• Removed .eslintrc and .eslintignore.
• Updated pnpm-lock.yaml.

Notes

• CI invokes pnpm lint / pnpm format through the repo Makefile, so no workflow files needed changing.
• Existing source is already oxfmt-clean and oxlint-clean — no source reformatting in this PR.

Verification

pnpm lint, pnpm format, pnpm build, and pnpm test:exports all succeed. (The mocha suite needs a local solana-test-validator and was not run in this environment; it is unaffected by the tooling change.)

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