[ZEPPELIN-6649] Add unit tests for the remaining shared utilities (shell + remote)

[huiseong29]

What is this PR for?

Adds unit tests for the three utilities left over in ZEPPELIN-6649, following the conventions in zeppelin-web-angular/AGENTS.md.

• isRecord (src/app/utility/type-utility.ts): the null and array boundaries, primitives, functions, and an object without a prototype.
• parseTableData (projects/zeppelin-react/src/utils/tableUtils.ts): header/rows split on tabs, header-only input, trailing newline, and an empty cell between tabs.
• exportFile (projects/zeppelin-react/src/utils/exportFile.ts): extends the existing spec with multi-row CSV assembly, the xlsx branch (file name, MIME type, and header plus rows read back from Sheet1), and the empty-data guard for xlsx and for data without rows.

Spec files only; no production code is changed. The files the issue lists as out of scope (element.ts, css-unit-conversion.ts, line-map.ts) are not touched.

Not pinned on purpose, since the baseline says not to record behaviour that is already questionable: parseTableData trims the whole input, so a leading empty header cell loses its tab ("\tb\n1\t2" gives ["b"]); CRLF input leaves a trailing \r on each cell at the end of a line; an empty string yields one empty column name. I can open a follow-up issue for these if useful.

What type of PR is it?

Improvement

Todos

• - Add unit tests for isRecord, parseTableData and exportFile

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-6649

How should this be tested?

• cd zeppelin-web-angular && npm run test:shell -- type-utility.spec.ts (10 tests)
• cd zeppelin-web-angular/projects/zeppelin-react && npm test && npm run lint (18 tests in src/utils)
• The React suite does not run in pull-request CI yet (see ZEPPELIN-6566), so it was run locally.

Screenshots (if appropriate)

Questions:

• Does the license files need to update? No.
• Is there breaking changes for older versions? No.
• Does this needs documentation? No.

[huiseong29]

The npm-audit check fails on braces (GHSA-vfj7-8cjw-p6xm), which zeppelin-react pulls in through micromatch -> http-proxy-middleware -> webpack-dev-server / ts-loader.

This PR only adds spec files under src/ and projects/zeppelin-react/src/utils/. It changes neither package.json nor the lockfile, so it does not affect the audited dependency tree.

Running npm audit --audit-level=high locally gives the same result. The flagged packages are all devDependencies, and npm audit --omit=dev --audit-level=high reports 0 vulnerabilities. The unit tests and lint for this change pass locally.

[voidmatcha]

LGTM 👍 Optional nit: assert the full XLSX media type rather than a substring.