Update OpenEXR and spill out its deps

[tad1]

Description

update OpenEXR to latest add IMath and Deflate submodule force OpenEXR to use local deps (IMath & Deflate) instead of using fetchContent

Testing

compiles Nabla w/ and w/o _NBL_COMPILE_WITH_OPEN_EXR_

TODO

• [x] make OpenEXR optional dep based on _NBL_COMPILE_WITH_OPEN_EXR_
• [ ] fix Deflate cmake warrnings; once again make OpenEXR use our Deflate
• [ ] remove unnecesary OpenEXR targets

[tad1]

currently, IMath & Deflate submodules point to OP's repo, @AnastaZIuk suggested to fork IMath; should Deflate also be forked?

[AnastaZIuk]

currently, IMath & Deflate submodules point to OP's repo, @AnastaZIuk suggested to fork IMath; should Deflate also be forked?

actually as long as we don't plan to modify their CMake we don't have to fork