Embed hash value in hash type entry

[zuiderkwast]

For a hash type key represented as a hash table, embed the field and value in one allocation when they together fit in the size of one cache line. For larger fields and values, another layout is used where the value is a separately allocated sds string.

This is a follow-up of #1502, where a field-value entry was created where the field is embedded and the value is a pointer to a separately allocated sds value.

[codecov]

Codecov Report

Attention: Patch coverage is 88.46154% with 12 lines in your changes missing coverage. Please review.

Project coverage is 70.99%. Comparing base (2d0b8e3) to head (cfe180b).

Files with missing lines	Patch %	Lines
src/t_hash.c	88.34%	12 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1579      +/-   ##
============================================
+ Coverage     70.94%   70.99%   +0.04%     
============================================
  Files           121      121              
  Lines         65132    65212      +80     
============================================
+ Hits          46207    46296      +89     
+ Misses        18925    18916       -9     

Files with missing lines	Coverage Δ
src/sds.c	86.87% <100.00%> (+0.18%)	⬆️
src/server.h	100.00% <ø> (ø)
src/t_hash.c	94.90% <88.34%> (-1.24%)	⬇️

... and 12 files with indirect coverage changes