Fix AliasName subcategory browse continuation

[MrAlaskan]

Summary

This PR fixes AliasNameClient.EnumerateSubCategoriesAsync() so it follows OPC UA Browse continuation points until the server has returned every SubAliasNameCategories reference, and adds a regression test covering the paged browse case that was previously truncated after the first page.

Problem

EnumerateSubCategoriesAsync() is intended to expose the full set of sub-categories organized beneath an AliasNameCategoryType node. However, the previous implementation only issued a single BrowseAsync() call and immediately enumerated BrowseResult.References from that first response.

Under OPC UA, servers are allowed to split browse results across multiple pages and return a ContinuationPoint when the first response does not contain the full reference set. In that situation, the client must continue with BrowseNext until the continuation point is exhausted. Because this helper never consumed the returned continuation point, it silently dropped every sub-category that appeared after the first page.

Changes

• Continue sub-category enumeration with BrowseNextAsync() whenever the initial BrowseAsync() response contains a non-empty continuation point.
• Keep the existing filtering behavior so the helper still returns only AliasNameCategoryType references that can be resolved to local NodeId values.
• Add scriptable Browse / BrowseNext support to the alias-name session test harness so paged browse behavior can be covered with a focused unit test.
• Add a regression test that verifies EnumerateSubCategoriesAsync() returns sub-categories from both the initial browse response and the follow-up BrowseNext response.

[marcschier]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.55%. Comparing base (84fa8e8) to head (9a45a7f).
⚠️ Report is 16 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4040      +/-   ##
==========================================
- Coverage   73.85%   73.55%   -0.31%     
==========================================
  Files        1345     1345              
  Lines      179988   180056      +68     
  Branches    31668    31682      +14     
==========================================
- Hits       132938   132444     -494     
- Misses      36299    36907     +608     
+ Partials    10751    10705      -46     

Files with missing lines	Coverage Δ
src/Opc.Ua.Client/AliasNames/AliasNameClient.cs	84.03% <100.00%> (+1.47%)	⬆️

... and 49 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.