chore:rename verifying singelton paymaster to sponsorship paymaster

[livingrockrises]

Summary

Only keep Sponsorship Paymaster (v2 version which charges premium)

Related Issue: # (issue number)

Change Type

• Bug Fix
• Refactor
• New Feature
• Breaking Change
• Documentation Update
• Performance Improvement
• Other

Checklist

• My code follows this project's style guidelines
• I've reviewed my own code
• I've added comments for any hard-to-understand areas
• I've updated the documentation if necessary
• My changes generate no new warnings
• I've added tests that prove my fix is effective or my feature works
• All unit tests pass locally with my changes
• Any dependent changes have been merged and published

Additional Information

Branch Naming

[linear]

SMA-351 Replace 'Verifying Paymaster' with 'Sponsorship Paymaster' References

Ensure all references to 'Verifying Paymaster' in our code are updated to 'Sponsorship Paymaster'.

[Aboudjem]

There are still some occurrences here:

File: ./contracts/token/BiconomyTokenPaymaster.sol
File: ./contracts/references/AdvancedVerifyingPaymaster.sol
File: ./contracts/sponsorship/SponsorshipPaymaster.sol

File: ./test/sponsorship-paymaster/biconomy-sponsorship-paymaster-specs.ts
File: ./test/bundler-integration/sponsorship-paymaster/biconomy-sponsorship-paymaster-specs.ts

There are also some instances of "VerifyingSigner" that should be renamed to align with the changes above

[livingrockrises]

There are still some occurrences here:

File: ./contracts/token/BiconomyTokenPaymaster.sol
File: ./contracts/references/AdvancedVerifyingPaymaster.sol
File: ./contracts/sponsorship/SponsorshipPaymaster.sol

File: ./test/sponsorship-paymaster/biconomy-sponsorship-paymaster-specs.ts
File: ./test/bundler-integration/sponsorship-paymaster/biconomy-sponsorship-paymaster-specs.ts

There are also some instances of "VerifyingSigner" that should be renamed to align with the changes above

There is no point of changing in the references.

Also verifyingSigner is a term it should be there as var name. Sponsorship paymaster uses a verifying signer