fix: group the boot ROM slot Pizza Boy SC fills

Read while walking the profile checklist on the profiles the
variant_group conversion touched.

- pizza-boy-sc: the core holds one Mega CD slot and one Master System
  slot, filled through the document picker under any name, and tests
  only the Mega CD length (libsc.so frontend/android/src/lib.rs:475,
  569-648, megacd_main_machine.rs:169-178). Nothing picks by
  territory, so the three images of each are a group, not a selection
  slot: megacd-boot-rom required, mastersystem-boot-rom optional.
- fpse, fpse-ng: the BIOS note pointed at "the other images of the
  group", a set the profile does not list. It now says any 524288-byte
  PlayStation image fills the slot.

emulators/fpse-ng.yml

@@ -149,7 +149,7 @@ files:
     md5: 924e392ed05558ffdb115408c263dccf
     sha1: 10155d8d6e6e832d6ea66db9bc098321fb5e8ebf
     description: "SCPH-1001, DTL-H1201, DTL-H3001 (v2.2 12-04-95 A)"
-    note: "The only image the code identifies, and it identifies it by a checksum of its own rather than by a hash it spells out: the 524288 bytes summed as signed bytes, accepted at 85958. The md5 and sha1 here are the dump that reproduces that sum. Selecting a BIOS by hand takes any .bin of exactly 524288 bytes, so the other images of the group fill the slot without being recognised by name or by sum."
+    note: "The only image the code identifies, and it identifies it by a checksum of its own rather than by a hash it spells out: the 524288 bytes summed as signed bytes, accepted at 85958. The md5 and sha1 here are the dump that reproduces that sum. Selecting a BIOS by hand takes any .bin of exactly 524288 bytes, so any other PlayStation image of that size fills the slot without being recognised by name or by sum."
     source_ref: "Main.java:24466-24487, Main.java:9945-9952, Main.java:30177-30192, Main.java:5392-5396, libfpse.so 0x70e20-0x70ed0"
 
   - name: kanji.rom

emulators/fpse.yml

@@ -121,7 +121,7 @@ files:
     md5: 924e392ed05558ffdb115408c263dccf
     sha1: 10155d8d6e6e832d6ea66db9bc098321fb5e8ebf
     description: "SCPH-1001, DTL-H1201, DTL-H3001 (v2.2 12-04-95 A)"
-    note: "The only image the code identifies, and it identifies it by a checksum of its own rather than by a hash it spells out: the 524288 bytes summed as signed bytes, accepted at 85958. The md5 and sha1 here are the dump that reproduces that sum. Selecting a BIOS by hand takes any file ending in .bin that is exactly 524288 bytes, so the other images of the group fill the slot without being recognised by name or by sum."
+    note: "The only image the code identifies, and it identifies it by a checksum of its own rather than by a hash it spells out: the 524288 bytes summed as signed bytes, accepted at 85958. The md5 and sha1 here are the dump that reproduces that sum. Selecting a BIOS by hand takes any file ending in .bin that is exactly 524288 bytes, so any other PlayStation image of that size fills the slot without being recognised by name or by sum."
     source_ref: "Main.java:4159-4175, Main.java:5919, Main.java:25217, res/raw/fpse.ini BiosName"
 
   - name: LibPS.exe

emulators/pizza-boy-sc.yml

@@ -85,12 +85,17 @@ notes: |
   box art, cheat, layout, sticker and per-ROM databases are created by their own
   CREATE TABLE.
 
+groups:
+  megacd-boot-rom:
+    required: true
+  mastersystem-boot-rom:
+    required: false
+
 files:
   - name: bios_CD_U.bin
     system: sega-megacd
-    required: true
+    group: megacd-boot-rom
     agnostic: true
-    selection_slot: "megacd-boot-rom"
     size: 131072
     validation: [size]
     description: "Sega CD boot ROM"
@@ -114,9 +119,8 @@ files:
 
   - name: bios_CD_E.bin
     system: sega-megacd
-    required: true
+    group: megacd-boot-rom
     agnostic: true
-    selection_slot: "megacd-boot-rom"
     size: 131072
     validation: [size]
     description: "Mega CD boot ROM"
@@ -127,9 +131,8 @@ files:
 
   - name: bios_CD_J.bin
     system: sega-megacd
-    required: true
+    group: megacd-boot-rom
     agnostic: true
-    selection_slot: "megacd-boot-rom"
     size: 131072
     validation: [size]
     description: "Mega CD boot ROM (Japan)"
@@ -140,9 +143,8 @@ files:
 
   - name: bios_U.sms
     system: sega-mastersystem
-    required: false
+    group: mastersystem-boot-rom
     agnostic: true
-    selection_slot: "mastersystem-boot-rom"
     description: "Master System boot ROM"
     note: >-
       Picked and stored like the Mega CD image and handed to the machine as a path.
@@ -155,9 +157,8 @@ files:
 
   - name: bios_E.sms
     system: sega-mastersystem
-    required: false
+    group: mastersystem-boot-rom
     agnostic: true
-    selection_slot: "mastersystem-boot-rom"
     description: "Master System boot ROM (Europe)"
     note: "Same slot and same absence of tests as the other Master System boot ROMs."
     source_ref: "Pizza Boy SC Basic 1.2.14 libsc.so frontend/android/src/lib.rs:590,
@@ -165,9 +166,8 @@ files:
 
   - name: bios_J.sms
     system: sega-mastersystem
-    required: false
+    group: mastersystem-boot-rom
     agnostic: true
-    selection_slot: "mastersystem-boot-rom"
     description: "Master System boot ROM (Japan)"
     note: "Same slot and same absence of tests as the other Master System boot ROMs."
     source_ref: "Pizza Boy SC Basic 1.2.14 libsc.so frontend/android/src/lib.rs:590,