feat(triple): remove old triple IDL mode switch

[chaojixinren]

Description

Fixes #3452

Based on #3451 (remove old triple implementation). With old triple (protocol/dubbo3) removed, the IDLMode compatibility switch used to distinguish IDL / non-IDL mode is no longer needed. This PR removes it and keeps only the minimal mode semantics required by new Triple.

Main changes:

• Remove IDLMode / IDL / NONIDL constants and the related WithIDL / WithIDLMode options from client and server
• Stop writing the IDLMode param onto the service URL
• Simplify TripleProtocol.Refer to always use NewTripleInvoker, and drop the old-triple NewDubbo3Invoker path and the isGenericCall helper
• Delete protocol/triple/dubbo3_invoker.go
• Decide IDL vs non-IDL mode by the presence of ServiceInfo (info != nil) instead of the IDLMode URL param
• Update related tests

Opened as a draft because it depends on #3451; the diff currently includes #3451's changes and will be rebased onto develop once #3451 is merged.

Checklist

• I confirm the target branch is develop
• Code has passed local testing
• I have added tests that prove my fix is effective or that my feature works

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
52.3% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.85%. Comparing base (8b5bbcf) to head (96d33cc).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
protocol/triple/server.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3460      +/-   ##
===========================================
+ Coverage    53.57%   54.85%   +1.28%     
===========================================
  Files          460      454       -6     
  Lines        35182    34799     -383     
===========================================
+ Hits         18847    19090     +243     
+ Misses       14857    14213     -644     
- Partials      1478     1496      +18     

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[chaojixinren]

ci 失败是因为 sample 还依赖 old triple
同#3451