Describe the bug
I recently helped discover some previously undocumented behaviour on the FDS. Bit 3 of $4030 reads return the value from bit 3 of $4025, which is the nametable arrangement/mirroring mode. I wrote a test program to verify the behaviour, and it fails on FCEUX. Mesen2 and Nestopia have since implemented the behaviour.

To Reproduce

1. Load the following test program: https://forums.nesdev.org/download/file.php?id=28216
2. Test fails for $4030.D3 R.

Expected behavior
Both tests should pass, as shown in this capture from a Twin Famicom:

(please complete the following information):

• EndeavourOS on 6.13.8-zen1-1-zen
• FCEUX Version 2.6.6 (QT)

Additional context
NESdev forum post: https://forums.nesdev.org/viewtopic.php?p=300488#p300488
Test program source code: https://github.com/TakuikaNinja/FDS-Mirroring-Test