Add icon validation for file size and duplicates

[Ramyromel]

Add validation for icon file size and duplicate icons.

• README.md

  • Add information about icon file size validation.
  • Add information about duplicate icon validation.

• .github/workflows/pr_checks.yml

  • Add validation for icon file size in the validate_icons job.
  • Add validation for duplicate icons in the validate_icons job.

• maintainer_checklist.md

  • Add a step to check for duplicate icons.
  • Add a step to check for icon file size.

• processor/src/main/kotlin/org/ethereum/lists/chains/Main.kt

  • Add logic to check for duplicate icons by calculating a hash (e.g., SHA-256) of each icon file.
  • Add logic to validate icon file size.

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[ligi]

Thanks - great contribution!
But the CI must pass and currently it fails on historic icons - so either an exception to them or they need to be converted to fit the new (and useful) constraints

[ligi]

would really love to get this merged - but not sure how to deal with the failing legacy
Maybe in step #1 just allow-list them so they do not fail so there is no new stuff coming in violating these constraints.
But then we also need to phase out old data ..

ideas welcome!

[ligi]

also looked into this a bit deeper - the "duplicate" thing is a bit weird to me - they should then also have the same IPFS CID right? Same content -> same CID

[ligi]

made a follow up PR here: #6386