fix: scientific notation price conversion bug

[CarsonRoscoe]

Description

There existed a bug with parseFloat where if the string had 7 or more decimals of precision (e.g. "$0.0000001"), it would convert to scientific notation format and bugout.

In practice, this is not much of an issue. Nanopayments are not economically feasible in the schemes today (as gas is more expensive than the amount transferred), and this is such a small number that it in fact rounds down to 0 if you tried to express it in a stablecoin with 6 decimals such as USDC or USDT. However, it is nonetheless a bug, and nanopayments will be more economically feasible once we complete development of the batch-settlement scheme

Tests

Added new unit tests to cover the fix

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits
• I added a changelog fragment for user-facing changes (docs-only changes can skip)

[vercel]

@CarsonRoscoe is attempting to deploy a commit to the Coinbase Team on Vercel.

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