fix(string,hash): use compact float format in IncrByFloat to match Redis

[songqing]

Previously, String::IncrByFloat and Hash::IncrByFloat used
std::to_string(double) to persist float values, which produces C-style
%f format with 6 fixed decimal places (e.g., "10.500000"). Redis uses a
compact %g-like format that strips trailing zeros (e.g., "10.5").

This caused GET/HGET after INCRBYFLOAT/HINCRBYFLOAT to return values
like "10.500000" instead of "10.5", breaking Redis protocol compatibility.

Replace std::to_string with util::Float2String (which uses fmt {:.17g})
in both String::IncrByFloat and Hash::IncrByFloat. The INCRBYFLOAT
command reply already used Float2String correctly; this fix aligns the
stored representation with both the reply format and Redis behavior.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
68.6% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud