Calculate tx fee on Rust side only if actual_fee from blockifier is 0

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 72.06%. Comparing base (bf96204) to head (a0008d9).

Files	Patch %	Lines
rpc/handlers.go	0.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1745 +/- ## ======================================= Coverage 72.05% 72.06% ======================================= Files 90 90 Lines 9724 9719 -5 ======================================= - Hits 7007 7004 -3 + Misses 2192 2189 -3 - Partials 525 526 +1 ```

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