ci: skip FP stability and convergence when no relevant files changed

Add a file-changes job (dorny/paths-filter) to both workflows so they
skip on PRs that only touch docs, CI config, or other non-code files.
Also register both workflow files in file-filter.yml so changes to
them trigger a run.

Author: sbryngelson

.github/file-filter.yml

@@ -30,6 +30,8 @@ yml: &yml
   - '.github/workflows/bench.yml'
   - '.github/workflows/test.yml'
   - '.github/workflows/formatting.yml'
+  - '.github/workflows/fp-stability.yml'
+  - '.github/workflows/convergence.yml'
 
 checkall: &checkall
   - *fortran_src

.github/workflows/convergence.yml

@@ -4,15 +4,36 @@ on:
   push:
     branches: [master]
   pull_request:
+    types: [opened, synchronize, reopened, ready_for_review]
   workflow_dispatch:
 
 env:
   OMPI_MCA_rmaps_base_oversubscribe: 1
 
 jobs:
+  file-changes:
+    name: Detect File Changes
+    runs-on: ubuntu-latest
+    outputs:
+      checkall: ${{ steps.changes.outputs.checkall }}
+    steps:
+      - name: Clone
+        uses: actions/checkout@v4
+
+      - name: Detect Changes
+        uses: dorny/paths-filter@v3
+        id: changes
+        with:
+          filters: ".github/file-filter.yml"
+
   convergence:
     name: "Convergence"
     runs-on: ubuntu-latest
+    needs: [file-changes]
+    if: >-
+      !cancelled() &&
+      needs.file-changes.result == 'success' &&
+      (needs.file-changes.outputs.checkall == 'true' || github.event_name == 'workflow_dispatch')
     timeout-minutes: 240
 
     steps:

.github/workflows/fp-stability.yml

@@ -35,9 +35,29 @@ on:
   workflow_dispatch:
 
 jobs:
+  file-changes:
+    name: Detect File Changes
+    runs-on: ubuntu-latest
+    outputs:
+      checkall: ${{ steps.changes.outputs.checkall }}
+    steps:
+      - name: Clone
+        uses: actions/checkout@v4
+
+      - name: Detect Changes
+        uses: dorny/paths-filter@v3
+        id: changes
+        with:
+          filters: ".github/file-filter.yml"
+
   fp-stability:
     name: Floating-Point Stability (Verrou)
     runs-on: ubuntu-latest
+    needs: [file-changes]
+    if: >-
+      !cancelled() &&
+      needs.file-changes.result == 'success' &&
+      (needs.file-changes.outputs.checkall == 'true' || github.event_name == 'workflow_dispatch')
 
     steps:
       - name: Clone