Get rid of math/overflow in stdlibs. Fix generate for git worktrees

gnovm/stdlibs/std/coins.gno

@@ -1,9 +1,6 @@
 package std
 
-import (
-	"math/overflow"
-	"strconv"
-)
+import "strconv"
 
 // NOTE: this is selectively copied over from tm2/pkgs/std/coin.go
 
@@ -56,13 +53,7 @@ func (c Coin) IsEqual(other Coin) bool {
 // An invalid result panics.
 func (c Coin) Add(other Coin) Coin {
 	mustMatchDenominations(c.Denom, other.Denom)
-
-	sum, ok := overflow.Add64(c.Amount, other.Amount)
-	if !ok {
-		panic("coin add overflow/underflow: " + strconv.Itoa(int(c.Amount)) + " +/- " + strconv.Itoa(int(other.Amount)))
-	}
-
-	c.Amount = sum
+	c.Amount += other.Amount
 	return c
 }
 
@@ -72,13 +63,7 @@ func (c Coin) Add(other Coin) Coin {
 // An invalid result panics.
 func (c Coin) Sub(other Coin) Coin {
 	mustMatchDenominations(c.Denom, other.Denom)
-
-	dff, ok := overflow.Sub64(c.Amount, other.Amount)
-	if !ok {
-		panic("coin sub overflow/underflow: " + strconv.Itoa(int(c.Amount)) + " +/- " + strconv.Itoa(int(other.Amount)))
-	}
-	c.Amount = dff
-
+	c.Amount -= other.Amount
 	return c
 }
 
@@ -113,10 +98,7 @@ func NewCoins(coins ...Coin) Coins {
 
 	for _, coin := range coins {
 		if currentAmount, exists := coinMap[coin.Denom]; exists {
-			var ok bool
-			if coinMap[coin.Denom], ok = overflow.Add64(currentAmount, coin.Amount); !ok {
-				panic("coin sub overflow/underflow: " + strconv.Itoa(int(currentAmount)) + " +/- " + strconv.Itoa(int(coin.Amount)))
-			}
+			coinMap[coin.Denom] = currentAmount + coin.Amount
 		} else {
 			coinMap[coin.Denom] = coin.Amount
 		}

misc/genstd/util.go

@@ -70,7 +70,8 @@ func findDirs() (gitRoot string, relPath string, err error) {
 	}
 	p := wd
 	for {
-		if s, e := os.Stat(filepath.Join(p, ".git")); e == nil && s.IsDir() {
+		// .git is normally a directory, or a file in case of a git worktree.
+		if _, e := os.Stat(filepath.Join(p, ".git")); e == nil {
 			// make relPath relative to the git root
 			rp := strings.TrimPrefix(wd, p+string(filepath.Separator))
 			// normalize separator to /