Fix: prevent calls from proxy admin in fuzz tests

[ChiTimesChi]

Description
SynapseClientUpgradeable tests assume that an upgradeable proxy is set up for the testing.
Some of the tests are fuzzing the caller address, and the proxy admin address should be excluded, as the calls from such address are not forwarded by the proxy. This PR fixes that.

PS. The testing contracts are being reworked in the upcoming PR, so the SynapseClientUpgradeable.t.sol file is left in its current not-so-pretty form intentionally.

[codecov]

Codecov Report

Merging #195 (e400139) into master (041e806) will increase coverage by 0.05811%.
The diff coverage is n/a.

@@                 Coverage Diff                 @@
##              master        #195         +/-   ##
===================================================
+ Coverage   50.62762%   50.68573%   +0.05810%     
===================================================
  Files            188         188                 
  Lines           8604        8604                 
  Branches          82          82                 
===================================================
+ Hits            4356        4361          +5     
+ Misses          3824        3819          -5     
  Partials         424         424                 

Impacted Files	Coverage Δ
agents/indexer/domain.go	52.72727% <0.00000%> (-14.54546%)	⬇️
services/scribe/backfill/contract.go	78.20513% <0.00000%> (+5.12820%)	⬆️
services/scribe/backfill/filter.go	74.69880% <0.00000%> (+6.02410%)	⬆️

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