Fix issue with single-digit expiry month not being preserved in PaymentSheet

[tillh-stripe]

Summary

This pull request fixes an issue where card expiration dates with a single-digit month weren’t preserved correctly when closing and re-opening a PaymentSheet via the FlowController.

Motivation

The issue came from converting the month input to an integer and then back to a string without preserving any leading zeros. As a result, 01/23 would turn into "123" instead of "0123", which was an invalid initial value for the expiration date element.

We’re doing this now with month.toString().padStart(length = 2, padChar = '0').

Testing

• Added tests
• Modified tests
• Manually verified

Screen recordings

Before

expiry-month-bug.mp4

After

expiry-month-fixed.mp4

Changelog

[Fixed] Card expiration dates with a single-digit month are now preserved correctly when closing and re-opening the PaymentSheet via the FlowController.

[github-actions]

Diffuse output:

OLD: paymentsheet-example-release-master.apk (signature: none)
NEW: paymentsheet-example-release-pr.apk (signature: none)

          │          compressed           │         uncompressed         
          ├───────────┬───────────┬───────┼───────────┬───────────┬──────
 APK      │ old       │ new       │ diff  │ old       │ new       │ diff 
──────────┼───────────┼───────────┼───────┼───────────┼───────────┼──────
      dex │  15.4 MiB │  15.4 MiB │ +17 B │  51.9 MiB │  51.9 MiB │ +8 B 
     arsc │   1.8 MiB │   1.8 MiB │   0 B │   1.8 MiB │   1.8 MiB │  0 B 
 manifest │     4 KiB │     4 KiB │   0 B │  18.5 KiB │  18.5 KiB │  0 B 
      res │ 873.3 KiB │ 873.3 KiB │   0 B │   1.4 MiB │   1.4 MiB │  0 B 
   native │   2.5 MiB │   2.5 MiB │   0 B │   5.9 MiB │   5.9 MiB │  0 B 
    asset │     3 MiB │     3 MiB │   0 B │     3 MiB │     3 MiB │  0 B 
    other │  81.7 KiB │  81.7 KiB │   0 B │ 155.6 KiB │ 155.6 KiB │  0 B 
──────────┼───────────┼───────────┼───────┼───────────┼───────────┼──────
    total │  23.6 MiB │  23.6 MiB │ +17 B │  64.1 MiB │  64.1 MiB │ +8 B 

         │          raw           │           unique            
         ├────────┬────────┬──────┼────────┬────────┬───────────
 DEX     │ old    │ new    │ diff │ old    │ new    │ diff      
─────────┼────────┼────────┼──────┼────────┼────────┼───────────
   files │      4 │      4 │    0 │        │        │           
 strings │ 250849 │ 250849 │    0 │ 213884 │ 213884 │ 0 (+0 -0) 
   types │  44261 │  44261 │    0 │  40627 │  40627 │ 0 (+0 -0) 
 classes │  37828 │  37828 │    0 │  37828 │  37828 │ 0 (+0 -0) 
 methods │ 221365 │ 221365 │    0 │ 213376 │ 213376 │ 0 (+0 -0) 
  fields │ 162804 │ 162804 │    0 │ 161764 │ 161764 │ 0 (+0 -0) 

 ARSC    │ old  │ new  │ diff 
─────────┼──────┼──────┼──────
 configs │  292 │  292 │  0   
 entries │ 6231 │ 6231 │  0

APK

   compressed    │ uncompressed │                
─────────┬───────┼───────┬──────┤                
 size    │ diff  │ size  │ diff │ path           
─────────┼───────┼───────┼──────┼────────────────
 3.2 MiB │ +17 B │ 9 MiB │ +8 B │ ∆ classes4.dex 
─────────┼───────┼───────┼──────┼────────────────
 3.2 MiB │ +17 B │ 9 MiB │ +8 B │ (total)