Override idls module to submodule to simplify idl update flow

[3vilhamster]

What changed?
Switched go mod for cadence-idls to submodule so we need to only update submodule when we want to updates idls.

Why?
Eliminate a confusion of separate version of idls used for thrift and proto and separate version used.

How did you test it?
make build/make test

Potential risks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.42%. Comparing base (45557d5) to head (ef9b405).
Report is 1 commits behind head on master.

Additional details and impacted files

see 1 file with indirect coverage changes

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[Groxx]

replaces do not work for anyone importing the client, so this only works for local developers

[Groxx]

while I like the idea and there might be something we can do to streamline this, I'm pretty confident this can't work the way we want it to. it'll just cause even-stranger issues when we make changes and fail to update one or the other, and they're less likely to be caught in CI since they'll only affect external users (due to replace).