refactor!: make VLenV2Codec private, add VLen{Array,Bytes,Utf8}Codec

[LDeakin]

Closes #115

[codecov]

Codecov Report

Attention: Patch coverage is 65.04854% with 36 lines in your changes missing coverage. Please review.

Project coverage is 81.61%. Comparing base (698fb83) to head (2b37e0a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ray/codec/array_to_bytes/vlen_v2/vlen_v2_macros.rs	65.21%	32 Missing ⚠️
zarrs/src/array/codec/array_to_bytes/vlen_v2.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #119      +/-   ##
==========================================
- Coverage   81.68%   81.61%   -0.08%     
==========================================
  Files         166      166              
  Lines       23756    23826      +70     
==========================================
+ Hits        19406    19445      +39     
- Misses       4350     4381      +31     

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