Intern all the instance ids in routing table

[Jackie-Jiang]

Within the routing table, instance ids (server ids) are repeated under each segment's routing entry. We explicitly intern them when reading them from InstanceConfig or IS/EV to reduce the memory footprint

[Copilot]

Pull request overview

This PR optimizes memory usage in routing tables by interning instance IDs (server IDs) that are frequently repeated across segment routing entries. The changes ensure instance IDs are interned when reading from InstanceConfig, IdealState, and ExternalView to reduce memory footprint.

Changes:

• Modified ServerInstance constructor to accept a pre-interned instance ID parameter
• Added string interning for instance IDs and states in IdealState and ExternalView ZNRecords
• Updated instance config processing to intern instance IDs before creating ServerInstance objects

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
pinot-core/src/main/java/org/apache/pinot/core/transport/ServerInstance.java	Refactored constructor to accept pre-interned instanceId parameter; preserved backward compatibility with @VisibleForTesting constructor
pinot-broker/src/main/java/org/apache/pinot/broker/routing/manager/BaseBrokerRoutingManager.java	Added internMapFields() method to intern instance IDs and states; integrated interning into IdealState/ExternalView loading and instance config processing

[codecov-commenter]

Codecov Report

❌ Patch coverage is 84.21053% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.18%. Comparing base (77a3dd6) to head (6ee8471).

Files with missing lines	Patch %	Lines
...rg/apache/pinot/core/transport/ServerInstance.java	71.42%	1 Missing and 1 partial ⚠️
...oker/routing/manager/BaseBrokerRoutingManager.java	91.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #17605      +/-   ##
============================================
+ Coverage     63.15%   63.18%   +0.03%     
  Complexity     1479     1479              
============================================
  Files          3173     3173              
  Lines        189917   189927      +10     
  Branches      29064    29064              
============================================
+ Hits         119935   120004      +69     
+ Misses        60658    60598      -60     
- Partials       9324     9325       +1     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (ø)
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	0.00% <ø> (ø)
java-11	63.15% <84.21%> (+0.01%)	⬆️
java-21	63.12% <84.21%> (+7.63%)	⬆️
temurin	63.18% <84.21%> (+0.03%)	⬆️
unittests	63.18% <84.21%> (+0.03%)	⬆️
unittests1	55.54% <57.14%> (+0.01%)	⬆️
unittests2	34.03% <84.21%> (+0.02%)	⬆️

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[Jackie-Jiang]

Seems the change is adding CPU overhead, and string deduplication can be achieved by XX:+UseStringDeduplication JVM option. Closing it