Expose `index-envs` library to public

[SeungheonOh]

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exposes index-envs to public

Resolves #6675

[SeungheonOh]

No clue why plutus-ir-test is failing. The change is literally a single line and unrelated to plutus-ir-test...

[effectfully]

No clue why plutus-ir-test is failing. The change is literally a single line and unrelated to plutus-ir-test...

Yeah, this has been causing trouble lately.

[SeungheonOh]

lmk if you need anything from me(though it's as minimal change as it will get) ; )