Implement strlen command

[danielealbano]

This PR implements the STRLEN commands and the related tests

[codecov]

Codecov Report

Base: 80.35% // Head: 80.48% // Increases project coverage by +0.13% 🎉

Coverage data is based on head (0f4a8b1) compared to base (00b8b28).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #214      +/-   ##
==========================================
+ Coverage   80.35%   80.48%   +0.13%     
==========================================
  Files         135      138       +3     
  Lines        8062     8150      +88     
==========================================
+ Hits         6478     6559      +81     
- Misses       1584     1591       +7     

Impacted Files	Coverage Δ
...module/redis/command/module_redis_command_strlen.c	100.00% <100.00%> (ø)
src/utils_string.c	58.70% <0.00%> (ø)
...c/module/redis/command/module_redis_command_scan.c	89.19% <0.00%> (ø)
...module/redis/command/module_redis_command_substr.c	93.10% <0.00%> (ø)
src/storage/db/storage_db.c	64.69% <0.00%> (+0.64%)	⬆️
...c/module/redis/command/module_redis_command_keys.c	88.89% <0.00%> (+1.39%)	⬆️

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