refactor(astutil): remove two more CountLeadingSpaces duplicates

listscan.leadingSpaces and requiredstructure.lineIndent were identical
copies of astutil.CountLeadingSpaces (body: len-TrimLeft with space-only
cutset) missed by the initial consolidation. Replace both with the
canonical helper.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Gj8AvSb7r12iqa7r3vYYof

Author: claude

internal/rules/listscan/listscan.go

@@ -27,7 +27,11 @@
 // (already in internal/lint/layer0.go) into this parser.
 package listscan
 
-import "bytes"
+import (
+	"bytes"
+
+	"github.com/jeduden/mdsmith/internal/rules/astutil"
+)
 
 // Item is one parsed list item.
 type Item struct {
@@ -180,7 +184,7 @@ func (p *parser) run() {
 // new list item, or a continuation line.
 func (p *parser) scanLine(i int, line []byte) int {
 	lineNo := i + 1
-	indent := leadingSpaces(line)
+	indent := astutil.CountLeadingSpaces(line)
 	markerToken := hasMarkerToken(line, indent)
 	interrupts := interruptsParagraph(line, indent)
 
@@ -672,10 +676,6 @@ func contentColumn(line []byte, afterMarker int) int {
 	return afterMarker + spaces
 }
 
-func leadingSpaces(line []byte) int {
-	return len(line) - len(bytes.TrimLeft(line, " "))
-}
-
 func isBlankLine(line []byte) bool {
 	for _, c := range line {
 		if c != ' ' && c != '\t' && c != '\r' {
@@ -735,7 +735,7 @@ func openingFenceRel(line []byte, indent, baseCol int) (fenceInfo, bool) {
 // fence run sits no more than 3 columns past fi.baseCol, runs >= fi.length
 // identical fence characters, and is followed only by whitespace.
 func closingFence(line []byte, fi fenceInfo) bool {
-	indent := leadingSpaces(line)
+	indent := astutil.CountLeadingSpaces(line)
 	if indent-fi.baseCol >= 4 {
 		return false
 	}
@@ -752,7 +752,7 @@ func closingFence(line []byte, fi fenceInfo) bool {
 // isThematicBreak reports whether line is a thematic break (3+ of a
 // single -, *, or _ with only spaces between), which is not a list item.
 func isThematicBreak(line []byte) bool {
-	indent := leadingSpaces(line)
+	indent := astutil.CountLeadingSpaces(line)
 	if indent >= 4 || indent >= len(line) {
 		return false
 	}

internal/rules/requiredstructure/rule.go

@@ -21,6 +21,7 @@ import (
 	"github.com/jeduden/mdsmith/internal/piparser"
 	"github.com/jeduden/mdsmith/internal/placeholders"
 	"github.com/jeduden/mdsmith/internal/rule"
+	"github.com/jeduden/mdsmith/internal/rules/astutil"
 	rulesettings "github.com/jeduden/mdsmith/internal/rules/settings"
 	"github.com/jeduden/mdsmith/internal/schema"
 	"github.com/jeduden/mdsmith/internal/yamlutil"
@@ -1437,7 +1438,7 @@ func fenceOpenRun(raw, lineB []byte) (byte, int) {
 	if len(lineB) == 0 || (lineB[0] != '`' && lineB[0] != '~') {
 		return 0, 0
 	}
-	if lineIndent(raw) > 3 {
+	if astutil.CountLeadingSpaces(raw) > 3 {
 		return 0, 0
 	}
 	n := fenceRun(lineB, lineB[0])
@@ -1452,7 +1453,7 @@ func fenceOpenRun(raw, lineB []byte) (byte, int) {
 // opener, nothing but the run on the trimmed line, and at most three
 // spaces of indentation.
 func fenceClose(raw, lineB []byte, ch byte, openLen int) bool {
-	if lineIndent(raw) > 3 {
+	if astutil.CountLeadingSpaces(raw) > 3 {
 		return false
 	}
 	n := fenceRun(lineB, ch)
@@ -1468,18 +1469,13 @@ func fenceRun(line []byte, ch byte) int {
 	return n
 }
 
-// lineIndent returns the number of leading spaces on the raw line.
-func lineIndent(raw []byte) int {
-	return len(raw) - len(bytes.TrimLeft(raw, " "))
-}
-
 // isPIOpenLine reports whether a raw body line opens a processing
 // instruction, mirroring the block parser in pkg/markdown: at most
 // three spaces of indentation, a `<?` opener, and a non-empty name
 // (the bytes up to the first whitespace or `?>`). An indented code
 // example showing a directive is therefore not mistaken for one.
 func isPIOpenLine(raw []byte) bool {
-	if lineIndent(raw) > 3 {
+	if astutil.CountLeadingSpaces(raw) > 3 {
 		return false
 	}
 	trimmed := bytes.TrimLeft(raw, " ")