[Prototype] attribute: Value.UnsafeAsSlice

[pellared]

d85e2dd

BenchmarkSlice/UnsafeAsSlice-20 	187695759	         6.335 ns/op	       0 B/op	       0 allocs/op

This would be very useful for the SDK to implement attribute limits so that we do not have heap allocations when introspecting the attributes.

Credits to @dashpole for the idea/proposal.

[codecov]

Codecov Report

❌ Patch coverage is 96.05263% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.7%. Comparing base (248da95) to head (d85e2dd).

Files with missing lines	Patch %	Lines
attribute/value.go	93.4%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7949   +/-   ##
=====================================
  Coverage   81.7%   81.7%           
=====================================
  Files        304     304           
  Lines      23287   23363   +76     
=====================================
+ Hits       19039   19110   +71     
- Misses      3862    3865    +3     
- Partials     386     388    +2     

Files with missing lines	Coverage Δ
attribute/hash.go	90.3% <100.0%> (+1.2%)	⬆️
attribute/internal/attribute.go	87.8% <100.0%> (+4.5%)	⬆️
attribute/key.go	100.0% <100.0%> (ø)
attribute/kv.go	100.0% <100.0%> (ø)
attribute/type_string.go	60.0% <ø> (ø)
attribute/value.go	92.8% <93.4%> (+0.2%)	⬆️

... and 3 files with indirect coverage changes

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