feat: platform-specific Limits extensions

[julio4]

The general idea is to be able to define extra limit fields per platform.
Example of an extension is provided for the Optimism platform to add data availability limits.

For this:

• extensions should implement LimitExtension and defined with new associated type ExtraLimits at platform level
• no extension can be defined with ()
• Limits is bounded by Platform generic ("limits of a platform")
• PlatformExecBounds is updated to have access to specific limit extension within pipeline steps