feat(cubesql): PlanNormalize - reduce stack allocations

[ovr]

Before optimizations

Dev Build (Debug, Unoptimized)

- Total allocations: 361
- Total stack size: 19,818 bytes (19.35 KB)

Release Build (Optimized)
- Total allocations: 187
- Total stack size: 11,429 bytes (11.16 KB)

Key Findings

1. Largest allocations are Expr types (144 bytes each):
   - Dev: 98 allocations = 14,112 bytes
   - Release: 52 allocations = 7,488 bytes
   - This is the datafusion::logical_expr::Expr enum
2. Debug builds have significant overhead:
   - 102 small allocations (8 bytes) reduced to 26 in release
   - 12 tiny allocations (1 byte) completely eliminated

After using Result<Box> as return type

Dev Build:
- Before: 19,818 bytes (19.35 KB)
- After: 12,572 bytes (12.28 KB)
- Improvement: 7,246 bytes saved (36.6% reduction)

Release Build:
- Before: 11,429 bytes (11.16 KB)
- After: 8,206 bytes (8.01 KB)
- Improvement: 3,223 bytes saved (28.2% reduction)

After using Expr as rt for grouping_set_normalize

Dev: -3.0% | Release: -2.6%

Dev Build:
- Before: 12,572 bytes (12.28 KB)
- After: 12,195 bytes (11.91 KB)

Release Build:
- Before: 8,206 bytes (8.01 KB)
- After: 7,990 bytes (7.80 KB)

Optimize binary_expr_normalize

Dev Build:
- Before: 5,054 bytes (55 allocations)
- After: 3,918 bytes (49 allocations)

Release Build:
- binary_expr_normalize: 3,918 bytes (3.83 KB)

Summary

Stage	Description	Stack Size	Reduction	binary_expr
1	Original Result<Expr>	11,429 bytes	baseline	-
2	Result<Box<Expr>>	8,206 bytes	-28.2%	-
3	grouping_set_normalize opt	7,990 bytes	-30.1%	5,054 bytes
4	binary_expr optimize	7,990 bytes	-30.1%	3,918 bytes

[codecov]

Codecov Report

❌ Patch coverage is 91.31944% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.15%. Comparing base (070e6e0) to head (e45516f).
⚠️ Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
...src/compile/engine/df/optimizers/plan_normalize.rs	90.31%	25 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #10055       +/-   ##
===========================================
+ Coverage   48.81%   77.15%   +28.33%     
===========================================
  Files         196      440      +244     
  Lines       15787    89270    +73483     
  Branches     3099     3099               
===========================================
+ Hits         7706    68873    +61167     
- Misses       7692    20008    +12316     
  Partials      389      389               

Flag	Coverage Δ
cube-backend	48.81% <ø> (ø)
cubesql	83.23% <91.31%> (?)

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