Deserialize the coverage files directly into the output files

[chkeita]

Summary of the Pull Request

The Coverage file was loading the output of the coverage in memory before writing it to the output file.
This could cause an increase in memory consumption. This change updates the logic to serialize the output directly in the output file without loading it in the memory.

closes #3420

[codecov-commenter]

Codecov Report

Merging #3410 (8a3e857) into main (9c4bc3e) will decrease coverage by 0.05%.
The diff coverage is 19.23%.

@@            Coverage Diff             @@
##             main    #3410      +/-   ##
==========================================
- Coverage   34.24%   34.20%   -0.05%     
==========================================
  Files         297      297              
  Lines       36365    36406      +41     
==========================================
- Hits        12453    12452       -1     
- Misses      23912    23954      +42     

Files Changed	Coverage Δ
...c/agent/onefuzz-file-format/src/coverage/binary.rs	66.66% <0.00%> (ø)
...gent/onefuzz-file-format/src/coverage/binary/v1.rs	51.85% <0.00%> (ø)
...c/agent/onefuzz-file-format/src/coverage/source.rs	66.66% <0.00%> (ø)
...gent/onefuzz-file-format/src/coverage/source/v1.rs	53.65% <0.00%> (ø)
...c/agent/onefuzz-task/src/tasks/coverage/generic.rs	0.00% <0.00%> (ø)
src/agent/cobertura/src/lib.rs	80.12% <77.27%> (-2.11%)	⬇️
src/agent/coverage/src/cobertura.rs	100.00% <100.00%> (ø)
src/agent/coverage/src/source.rs	91.57% <100.00%> (-0.09%)	⬇️