feat(mrml-core): create multi include loader

[codecov[bot]]

Codecov Report

Merging #322 (50507c2) into main (192fadf) will increase coverage by 0.06%. Report is 2 commits behind head on main. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #322      +/-   ##
==========================================
+ Coverage   93.21%   93.27%   +0.06%     
==========================================
  Files         230      231       +1     
  Lines       12136    12240     +104     
==========================================
+ Hits        11312    11417     +105     
+ Misses        824      823       -1     

Files Changed	Coverage Δ
...ckages/mrml-core/src/prelude/parser/http_loader.rs	97.04% <ø> (ø)
...kages/mrml-core/src/prelude/parser/local_loader.rs	96.42% <ø> (ø)
packages/mrml-core/src/prelude/parser/mod.rs	77.77% <ø> (ø)
packages/mrml-core/src/mj_head/render.rs	97.31% <100.00%> (ø)
...kages/mrml-core/src/prelude/parser/multi_loader.rs	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes