fix(instanceset): normalize planner role priorities

[leon-ape]

What changed

• normalize every InstanceSet role-priority lookup before reading the lower-case priority map
• preserve BestEffortParallel quorum layers when ReplicaRole.Name uses mixed case
• add a regression test covering mixed-case follower and leader roles across the actual update layers

Why

ComposeRolePriorityMap stores role names in lower case, but the BestEffort planner calculated its quorum and leader thresholds with the original ReplicaRole.Name. Names such as Follower and Leader therefore resolved to the default priority and could place multiple quorum members in the same update layer.

This is the InstanceSet counterpart to #10677.

Validation

go test ./pkg/controller/instanceset -count=1

Fixes #10641

[apecloud-bot]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.05%. Comparing base (b1e0fcf) to head (5b8205b).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10700      +/-   ##
==========================================
+ Coverage   63.94%   64.05%   +0.11%     
==========================================
  Files         520      520              
  Lines       63013    63014       +1     
==========================================
+ Hits        40291    40363      +72     
+ Misses      19116    19059      -57     
+ Partials     3606     3592      -14     

Flag	Coverage Δ
unittests	64.05% <100.00%> (+0.11%)	⬆️

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[leon-ape]

/approve

[apecloud-bot]

/cherry-pick release-1.1

[apecloud-bot]

🤖 says: cherry pick action finished successfully 🎉!
See: https://github.com/apecloud/kubeblocks/actions/runs/29896873672