fix: event message subscription subscription broker

[Larkooo]

addresses a bug where the event messages subscription service uses the broker item as entities and thus, messes up when the subscription update fires

[codecov]

Codecov Report

Attention: Patch coverage is 7.14286% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 70.37%. Comparing base (c8815a9) to head (625c852).

Files	Patch %	Lines
crates/torii/graphql/src/object/event_message.rs	0.00%	10 Missing ⚠️
crates/torii/core/src/sql.rs	0.00%	2 Missing ⚠️
crates/torii/core/src/types.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1885      +/-   ##
==========================================
- Coverage   70.38%   70.37%   -0.01%     
==========================================
  Files         315      315              
  Lines       35761    35766       +5     
==========================================
  Hits        25169    25169              
- Misses      10592    10597       +5     

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[glihm]

We should consider doing a document / mapping or what's Torii is doing with the different brokers / subscriptions system. Let's catch up on that @Larkooo. :)