Draft: Datagen validation for currency vs decimal pattern grouping

[younies]

Description

This is a draft PR intended to demonstrate our findings regarding the consistency of digit grouping between decimal and currency patterns in CLDR.

We have added a validation check to the currency data generator (validate_integer_structures in provider/source/src/currency/essentials.rs) that compares the integer structure (grouping sizes and digit placeholders) of all currency patterns (standard, accounting, and their alphaNextToNumber variants) against the locale's standard decimal pattern.

Findings

1. Core Consistency: For almost all locales, the core numeric grouping matches exactly between decimal and currency patterns (e.g., both use #,##0 in en, and #,##,##0 in bn).
2. Exceptions/Mismatches: We identified a mismatch in the ccp (Chakma) locale:
   • Decimal Standard: #,##,##0.### (Indian grouping)
   • Currency Standard: #,##,##0.00¤ (Indian grouping)
   • Currency alphaNextToNumber (standard and accounting): ¤ #,##0.00 (Western grouping: #,##0)
   • This seems to be an inconsistency in CLDR.

Changelog

• Adds integer_structure to NumberPattern to extract grouping/digit placeholders.
• Adds validate_integer_structures in essentials.rs to assert equality during datagen.
• Adds an exception for ccp to print a WARNING instead of failing the build, allowing tests to pass.

This PR is a demonstration of the validation logic and the CLDR consistency.