chore(tests-sdk): switch @lazorkit/sdk-legacy from file: link to ^0.3.1

Drops the cross-repo file: link that pointed at the sibling
lazorkit-protocol checkout. The link was a development convenience while
sdk-legacy was unpublished; now that 0.3.1 is on npm, tests-sdk depends
on it the same way an external integrator would.

Why this matters:
- CI no longer needs the lazorkit-protocol checkout to install
  tests-sdk deps. The dropped tsc (tests-sdk) lint job can be restored
  in a follow-up.
- This is the canonical consumer test for the published package: 65/65
  vitest E2E pass against the foundation devnet binary using the npm
  tarball, which proves the published artifact is byte-equivalent to
  the source at lazorkit-protocol/sdk/sdk-legacy.

Verification:
- Smoke test in clean dir: npm i @lazorkit/sdk-legacy@0.3.1 + import
  LazorKitClient/Actions/serializeActions/AuthorityAccount/SessionAccount
  /ed25519/session/PROGRAM_ID_* — all resolve and behave correctly.
- tests-sdk: npm install resolves to registry tarball (verified in
  package-lock.json: resolved=https://registry.npmjs.org/...0.3.1.tgz).
- Local validator + npx vitest run: 65/65 pass (12 test files).

Author: onspeedhp