[Stripe Issuing] Set buffer to $250k (#12149)

## Summary of the problem

<img width="1166" height="319" alt="image"
src="https://github.com/user-attachments/assets/c7188e74-2871-4fcb-a8e7-434838b61ddf"
/>

We're starting to use a good portion of our buffer

## Describe your changes

Bump to $250k

Author: garyhtou

app/jobs/topup_stripe_job.rb

@@ -23,7 +23,7 @@ def perform
     # money on Stripe Issuing is at least two weeks.
     # Ex. The money from a top-up today will be spent in no earlier than two
     #     weeks from now (FIFO order).
-    buffer = 200_000 * 100
+    buffer = 250_000 * 100
 
     # amount of money currently in stripe
     balances = StripeService::Balance.retrieve