Function dedup conf decode

[xunilrj]

Description

This PR improves fn_dedup to also deduplicate config decode functions.

Given how early this optimization was running, some optimizations were being lost, because some functions only get identical at the final IR. I believe we chose to run this early to decrease the pressure in other passes, but to allow this pass to really coalesce decodes I think makes sense to run it again at the end.

I am also deleting from the IR functions that were being replaced. This allowed the new test to decrease around 100 bytes. Our old configurable test went from 7600 to 7250 bytes.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[codspeed-hq]

CodSpeed Performance Report

Merging #6623 will degrade performances by 16.23%

_{Comparing xunilrj/fn-dedup-conf-decode (0324443) with master (79170db)}

Summary

❌ 1 regressions
✅ 21 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	master	xunilrj/fn-dedup-conf-decode	Change
❌	document_symbol	4.4 ms	5.2 ms	-16.23%