feat(snaps-rpc-methods): Use BigInt to parse chain ids

[rekmarks]

There are no size limits on Ethereum chain ids, so we should use BigInt to parse them.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.43%. Comparing base (824fd4f) to head (c5d0161).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2781   +/-   ##
=======================================
  Coverage   94.43%   94.43%           
=======================================
  Files         483      483           
  Lines       10297    10297           
  Branches     1568     1568           
=======================================
  Hits         9724     9724           
  Misses        573      573           

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