fix[codegen]: fix false positive in risky call detection

[charles-cooper]

the potential_overlap and read_write_overlap() functions use contains_risky_call to detect if there is potential for reentrancy. however, when the target is a precompile, there is no chance for reentrancy, so we filter them out of the detector.

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[codecov[bot]]

Codecov Report

Attention: Patch coverage is 63.63636% with 4 lines in your changes missing coverage. Please review.

Project coverage is 43.85%. Comparing base (4594f8b) to head (48132c9).

Files	Patch %	Lines
vyper/codegen/ir_node.py	63.63%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #4160 +/- ## =========================================== - Coverage 91.34% 43.85% -47.50% =========================================== Files 109 109 Lines 15606 15616 +10 Branches 3432 3434 +2 =========================================== - Hits 14256 6849 -7407 - Misses 920 8251 +7331 - Partials 430 516 +86 ```

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