Proto/SR: update constants to 10sec block time

Context

Because of !11288 (merged), we have to update our constants. This merge request changes the default parameters to take the new block time into account, and also update mainnet constants. It now computes the constants based on the block time programatically.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR