Add static analyzer to discourage use of panic() (#15075)

* Implement static analysis to prevent panics

* Add nopanic to nogo

* Fix violations and add exclusions

Fix violations and add exclusions for all

* Changelog fragment

* Use pass.Report instead of pass.Reportf

* Remove strings.ToLower for checking init method name

* Add exclusion for herumi init

* Move api/client/beacon template function to init and its own file

* Fix nopanic testcase

time/slots/slotticker.go

@@ -75,6 +75,8 @@ func (s *SlotIntervalTicker) Done() {
 }
 
 // NewSlotTicker starts and returns a new SlotTicker instance.
+// This method panics if genesis time is zero.
+// lint:nopanic -- Communicated panic in godoc commentary.
 func NewSlotTicker(genesisTime time.Time, secondsPerSlot uint64) *SlotTicker {
 	if genesisTime.IsZero() {
 		panic("zero genesis time")
@@ -89,6 +91,8 @@ func NewSlotTicker(genesisTime time.Time, secondsPerSlot uint64) *SlotTicker {
 
 // NewSlotTickerWithOffset starts and returns a SlotTicker instance that allows a offset of time from genesis,
 // entering a offset greater than secondsPerSlot is not allowed.
+// This method will panic if genesis time is zero or the offset is less than seconds per slot.
+// lint:nopanic -- Communicated panic in godoc commentary.
 func NewSlotTickerWithOffset(genesisTime time.Time, offset time.Duration, secondsPerSlot uint64) *SlotTicker {
 	if genesisTime.Unix() == 0 {
 		panic("zero genesis time")
@@ -176,6 +180,8 @@ func (s *SlotIntervalTicker) startWithIntervals(
 // several offsets of time from genesis,
 // Caller is responsible to input the intervals in increasing order and none bigger or equal than
 // SecondsPerSlot
+// This method will panic if genesis time is zero, intervals is 0 length, or offsets are invalid.
+// lint:nopanic -- Communicated panic in godoc commentary.
 func NewSlotTickerWithIntervals(genesisTime time.Time, intervals []time.Duration) *SlotIntervalTicker {
 	if genesisTime.Unix() == 0 {
 		panic("zero genesis time")

time/slots/slottime.go

@@ -126,7 +126,7 @@ func EpochStart(epoch primitives.Epoch) (primitives.Slot, error) {
 func UnsafeEpochStart(epoch primitives.Epoch) primitives.Slot {
 	es, err := EpochStart(epoch)
 	if err != nil {
-		panic(err)
+		panic(err) // lint:nopanic -- Unsafe is implied and communicated in the godoc commentary.
 	}
 	return es
 }