Fix Foundry artifact paths

[pmikolajczyk41]

Newer Foundry distributions put path to the artifact's json under <Solidity version> / "default" / "path". Without that fix, current CLI fails with:

Using workspace "Playground"
Detected Foundry project for /my-foundry-project
node:internal/errors:496
    ErrorCaptureStackTrace(err);
    ^

TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received an instance of Object
    at new NodeError (node:internal/errors:405:5)
    at validateString (node:internal/validators:162:11)
    at Object.join (node:path:1171:7)
    at readFoundrySolidityCache (/usr/local/lib/node_modules/ethernal/bin/index.js:459:30)
    at FSWatcher.<anonymous> (/usr/local/lib/node_modules/ethernal/bin/index.js:488:35)
    at FSWatcher.emit (node:events:517:28)
    at FSWatcher.emitWithAll (/usr/local/lib/node_modules/ethernal/node_modules/chokidar/index.js:540:8)
    at FSWatcher._emit (/usr/local/lib/node_modules/ethernal/node_modules/chokidar/index.js:632:8)
    at NodeFsHandler._handleFile (/usr/local/lib/node_modules/ethernal/node_modules/chokidar/lib/nodefs-handler.js:400:14)
    at NodeFsHandler._addToNodeFs (/usr/local/lib/node_modules/ethernal/node_modules/chokidar/lib/nodefs-handler.js:637:21) {
  code: 'ERR_INVALID_ARG_TYPE'
}