Add function field schema wrapper

[shanghaikid]

Summary

• add alterCollectionSchema wrapper for Milvus 3.0-beta function field schema changes
• add addFunctionField convenience wrapper with BM25 sparse output validation
• add e2e coverage for success paths, string enum input, and validation failures

Tests

• NODE_ENV=dev npx jest test/grpc/FullTextSearch.spec.ts --runInBand
• NODE_ENV=dev npx jest test/grpc/FullTextSearch.spec.ts --runInBand --coverage --collectCoverageFrom=milvus/grpc/Collection.ts --collectCoverageFrom=milvus/types/Collection.ts --collectCoverageFrom=milvus/const/error.ts --coverageReporters=json --coverageReporters=json-summary --coverageReporters=text
• changed statements: 28/28 = 100.00%
• changed branches: 17/17 = 100.00%
• npm run build

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: shanghaikid

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.54%. Comparing base (85c757f) to head (888cfb0).
⚠️ Report is 44 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #578      +/-   ##
==========================================
+ Coverage   97.27%   97.54%   +0.27%     
==========================================
  Files          60       63       +3     
  Lines        4620     5060     +440     
  Branches     1309     1492     +183     
==========================================
+ Hits         4494     4936     +442     
- Misses        121      124       +3     
+ Partials        5        0       -5     

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