Fix calldata validation for tuple types

[emdin]

Summary

• Custom action form validation rejected all tuple and tuple[] parameter types, blocking proposals with struct-based function parameters (e.g. diamondCut's FacetCut[])
• isValidSingleValue had no case for tuple, falling through to default: return false
• isValidCalldataValue rejected empty arrays for tuple[], which is valid (e.g. empty facet cuts)

Test plan

• Create a custom action proposal targeting a Diamond contract and selecting diamondCut method
• Verify the red validation dot no longer appears on the Custom section when tuple params are present
• Verify "Add Action" is no longer blocked by tuple validation
• Verify non-tuple parameter validation still works correctly

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