feat: implement mutarrayview

[Yu-zh]

This PR Implements MutArrayView[T], a zero-copy mutable view type that provides read-write access to array slices without copying data.

Major Changes:

• New type: MutArrayView[T] - a builtin valtype representing a mutable window into arrays
• Core operations:
  • Element access: at()/[] and set()/[]= with bounds checking
  • Unsafe operations: unsafe_get() and unsafe_set() for performance-critical code
  • View creation: mut_sub() method for Arrays, FixedArrays, and MutArrayViews
  • Read-only conversion: sub()/[:] to convert to immutable ArrayView
• Iterator support: Added iterator(), rev_iterator(), and iterator2() implementations
• Trait implementations: Show, Eq, Compare, and Hash
• Negative index support: Enables Python-style negative indexing (e.g., arr.mut_sub(start=-3, end=-1))
• For the rest of APIs that ArrayView[T] has but not implemented for MutArrayView[T], user can first take view from MutArrayView[T] and then use ArrayView[T]'s API.

[coveralls]

Pull Request Test Coverage Report for Build 1688

Details

• 34 of 55 (61.82%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.04%) to 89.763%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
builtin/mutarrayview.mbt	34	38	89.47%
array/mutview.mbt	0	17	0.0%

Totals
Change from base Build 1687:	-0.04%
Covered Lines:	9979
Relevant Lines:	11117

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💛 - Coveralls