feat(1840): Use "decimal" format instead of "hexadecimal" format for "chain_id" event property

[DDDDDanica]

Description

Migrated from original PR due to conflict
#24203.

This PR standardizes the chain_id event property in metrics tracking by converting hexadecimal chain IDs to decimal format. This ensures consistent data representation across our analytics platform while maintaining compatibility with all existing chain ID formats.

Context:
The extension codebase currently uses multiple chain ID formats:

• Hexadecimal (e.g., "0x1" for Ethereum Mainnet)
• Decimal (e.g., "1")
• CAIP chain IDs (following the format "namespace:reference", e.g., "eip155:1")

Rather than modifying each individual event tracking call, this approach centralizes the format standardization logic, making our codebase more maintainable and our metrics more consistent.

Related issues

Fixes: https://github.com/MetaMask/MetaMask-planning/issues/1840

Manual testing steps

1. Go to this page...

Screenshots/Recordings

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[DDDDDanica]

The data team doesn't want us to convert chainId in segment to decimal. But it sounds like they will want us to send an extra field for non-ethereum chains in the future (chain_id_caip).

=> Close until requirement to be defined