[Vault] Merge VaultAdmin and VaultCore

[clement-ux]

Description

Merge VaultAdmin and VaultCore.

• This PR remove the old proxy implementation, where VaultCore delegated calls to VaultAdmin. Now VaultAdmin directly inherit from VaultCore.
• This allow a simpler inherance graph, less hurdles to understand how contracts relationship works.
• This PR renames previous vaults to only OTokenVault.
• This PR migrate zapper to dedicated folder.

Before:

After

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 35.26%. Comparing base (8b073b8) to head (617b187).

Files with missing lines	Patch %	Lines
contracts/contracts/vault/OETHPlumeVault.sol	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           clement/simplify-ousd    #2743      +/-   ##
=========================================================
- Coverage                  35.51%   35.26%   -0.25%     
=========================================================
  Files                        128      124       -4     
  Lines                       5471     5450      -21     
  Branches                    1443     1440       -3     
=========================================================
- Hits                        1943     1922      -21     
  Misses                      3527     3527              
  Partials                       1        1              

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