Improvements to code quality and readability (#1737)

* Remove 1 unused field and 3 unused functions

unused elements fount by running
golangci-lint run --disable-all --enable unused

src/result.go:19:2: field `index` is unused (unused)
        index  int32
        ^
src/tui/light.go:716:23: func `(*LightWindow).stderr` is unused (unused)
func (w *LightWindow) stderr(str string) {
                      ^
src/terminal.go:1015:6: func `numLinesMax` is unused (unused)
func numLinesMax(str string, max int) int {
     ^
src/tui/tui.go:167:20: func `ColorPair.is24` is unused (unused)
func (p ColorPair) is24() bool {
                   ^

* Address warnings from "gosimple" linter

src/options.go:389:83: S1003: should use strings.Contains(str, ",,,") instead (gosimple)
        if str == "," || strings.HasPrefix(str, ",,") || strings.HasSuffix(str, ",,") || strings.Index(str, ",,,") >= 0 {
                                                                                         ^
src/options.go:630:18: S1007: should use raw string (`...`) with regexp.MustCompile to avoid having to escape twice (gosimple)
        executeRegexp = regexp.MustCompile(
                        ^
src/terminal.go:29:16: S1007: should use raw string (`...`) with regexp.MustCompile to avoid having to escape twice (gosimple)
        placeholder = regexp.MustCompile("\\\\?(?:{[+sf]*[0-9,-.]*}|{q}|{\\+?f?nf?})")
                      ^
src/terminal_test.go:92:10: S1007: should use raw string (`...`) with regexp.MustCompile to avoid having to escape twice (gosimple)
        regex = regexp.MustCompile("\\w+")
                ^

* Address warnings from "staticcheck" linter

src/algo/algo.go:374:2: SA4006: this value of `offset32` is never used (staticcheck)
        offset32, T := alloc32(offset32, slab, N)
        ^
src/algo/algo.go:456:2: SA4006: this value of `offset16` is never used (staticcheck)
        offset16, C := alloc16(offset16, slab, width*M)
        ^
src/tui/tui.go:119:2: SA9004: only the first constant in this group has an explicit type (staticcheck)
        colUndefined Color = -2
        ^

1 files changed, 2 insertions, 2 deletions

diff --git a/src/algo/algo.go b/src/algo/algo.go
index 2fe5c091..a627514c 100644
--- a/src/algo/algo.go
+++ b/src/algo/algo.go
@@ -371,7 +371,7 @@ func FuzzyMatchV2(caseSensitive bool, normalize bool, forward bool, input *util.
 	// The first occurrence of each character in the pattern
 	offset32, F := alloc32(offset32, slab, M)
 	// Rune array
-	offset32, T := alloc32(offset32, slab, N)
+	_, T := alloc32(offset32, slab, N)
 	input.CopyRunes(T)
 
 	// Phase 2. Calculate bonus for each point
@@ -453,7 +453,7 @@ func FuzzyMatchV2(caseSensitive bool, normalize bool, forward bool, input *util.
 	copy(H, H0[f0:lastIdx+1])
 
 	// Possible length of consecutive chunk at each position.
-	offset16, C := alloc16(offset16, slab, width*M)
+	_, C := alloc16(offset16, slab, width*M)
 	copy(C, C0[f0:lastIdx+1])
 
 	Fsub := F[1:]