Run fuzzer daily

Waiting for the fuzzer slows down the dev feedback loop because it makes
CI slow. We still want fuzz coverage but not in a way that slows down
devs.

Instead of running the fuzzer on every PR just run it once a nightly.

As we do for other daily jobs, rename the yaml file to make explicit
what it does.

Open questions:

- This should run for 30 minutes but I can't work out why the current
  set up only runs for a shorter time than that?
- Is this less fuzzing i.e., is 30 minutes once a day better or worse that 1
  minute 30 times?

.github/workflows/cron-daily-fuzz.yml

@@ -1,12 +1,12 @@
 # Automatically generated by fuzz/generate-files.sh
 name: Fuzz
-
 on:
-  push:
+  schedule:
-    branches:
+    # 5am every day UTC, this correlates to:
-      - master
+    # - 10pm PDT
-      - 'test-ci/**'
+    # - 6am CET
-  pull_request:
+    # - 4pm AEDT
+    - cron: '00 05 * * *'
 
 jobs:
   fuzz:
@@ -15,6 +15,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        # We only get 20 jobs at a time, we probably don't want to go
+        # over that limit with fuzzing because of the hour run time.
         fuzz_target: [
           bitcoin_deserialize_address,
           bitcoin_deserialize_block,

fuzz/fuzz.sh

@@ -28,7 +28,7 @@ for targetFile in $targetFiles; do
   else
     HFUZZ_INPUT_ARGS=""
   fi
-  HFUZZ_RUN_ARGS="--run_time 30 --exit_upon_crash -v $HFUZZ_INPUT_ARGS" cargo hfuzz run "$targetName"
+  HFUZZ_RUN_ARGS="--run_time 3600 --exit_upon_crash -v $HFUZZ_INPUT_ARGS" cargo hfuzz run "$targetName"
 
   checkReport "$targetName"
 done