Disable STX if a regular tx is in progress

[dan437]

Explanation

We can't allow STX if a regular tx is in progress, otherwise there could be a nonce issue.

Screenshots/Screencaps

Warning notification:

Disabled STX button + tooltip explanation:

Manual testing steps

• Do a non-STX swap with the lowest gas limit and low fees per gas, that way you will have a regular tx in progress for a while
• Try to do a smart transaction, it will be disabled

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[darkwing]

Could we instead do this to prevent large nesting?

if (transactions?.length < 0) {
return;
}