[Bug]: Unknown error in send flow when sending close to max Solana but not max

View issue in GitHub: https://github.com/MetaMask/metamask-mobile/issues/20759

View issue in GitHub: https://github.com/MetaMask/metamask-mobile/issues/20759

View issue in GitHub: https://github.com/MetaMask/metamask-mobile/issues/20759

**Describe the bug**

When trying to send max Solana, I get a valid simulation error that there is not enough Solana to cover fees. However, if I try to send close to max, but still low enough that I should be able to cover fees, I get "unknown error." Also, sometimes the send flow sheet hangs with no response. See video.

**Expected behavior**

Never get an unknown error, never get a hanging send flow.

**Screenshots/Recordings**

https://github.com/user-attachments/assets/1129ce59-e5ca-4b6e-84e7-c06959e9c362

**Steps to reproduce**

1. Go to send flow
2. Attempt to send max Solana (manually entering amount)
3. Observe you cannot send
4. Go back and attempt to send close to max
5. Observe you get "unknown error"
6. Go back and attempt to send a small amount
7. Observe there are no errors, you can proceed

**Error messages or log output**

```shell

```

**Detection stage**

During release testing

**Version**

7.57.0 (2630)

**Build type**

Other (please specify exactly where you obtained this build in "Additional Context" section)

**Device**

iPhone 16

**Operating system**

iOS

Start by reproducing the send flow on iOS with Solana using the three amounts described: max, near-max, and small. No source files or tests are named, so trace the send-flow entry point and capture the error or hang behavior for version 7.57.0; done means near-max sends either proceed when fees are covered or show a specific, non-hanging error.

Written by the indexing model from the issue text.