parser/pageparser: Store shortcode names as unique.Handle[string] to save memory allocations

```
                        │ stash.bench  │        perf-pagelexer.bench        │
                        │    sec/op    │    sec/op     vs base              │
ShortcodeLexer-10         68.87µ ± ∞ ¹   65.91µ ± ∞ ¹       ~ (p=0.200 n=4)
Parse-10                  7.421µ ± ∞ ¹   7.030µ ± ∞ ¹  -5.28% (p=0.029 n=4)
HasShortcode/Match-10     70.42n ± ∞ ¹   77.37n ± ∞ ¹  +9.86% (p=0.029 n=4)
HasShortcode/NoMatch-10   14.32n ± ∞ ¹   14.38n ± ∞ ¹       ~ (p=0.086 n=4)
geomean                   847.2n         847.3n        +0.01%
¹ need >= 6 samples for confidence interval at level 0.95

                        │  stash.bench  │         perf-pagelexer.bench          │
                        │     B/op      │     B/op       vs base                │
ShortcodeLexer-10         181.3Ki ± ∞ ¹   177.4Ki ± ∞ ¹  -2.19% (p=0.029 n=4)
Parse-10                  24.56Ki ± ∞ ¹   24.19Ki ± ∞ ¹  -1.53% (p=0.029 n=4)
HasShortcode/Match-10       0.000 ± ∞ ¹     0.000 ± ∞ ¹       ~ (p=1.000 n=4) ²
HasShortcode/NoMatch-10     0.000 ± ∞ ¹     0.000 ± ∞ ¹       ~ (p=1.000 n=4) ²
geomean                               ³                  -0.93%               ³
¹ need >= 6 samples for confidence interval at level 0.95
² all samples are equal
³ summaries must be >0 to compute geomean

                        │ stash.bench  │         perf-pagelexer.bench         │
                        │  allocs/op   │  allocs/op   vs base                 │
ShortcodeLexer-10         1004.0 ± ∞ ¹   921.0 ± ∞ ¹   -8.27% (p=0.029 n=4)
Parse-10                   34.00 ± ∞ ¹   14.00 ± ∞ ¹  -58.82% (p=0.029 n=4)
HasShortcode/Match-10      0.000 ± ∞ ¹   0.000 ± ∞ ¹        ~ (p=1.000 n=4) ²
HasShortcode/NoMatch-10    0.000 ± ∞ ¹   0.000 ± ∞ ¹        ~ (p=1.000 n=4) ²
```

Author: bep

parser/pageparser/pagelexer.go

@@ -18,6 +18,7 @@ import (
 	"fmt"
 	"unicode"
 	"unicode/utf8"
+	"unique"
 )
 
 const eof = -1
@@ -78,7 +79,7 @@ func newPageLexer(input []byte, stateStart stateFunc, cfg Config) *pageLexer {
 		lexerShortcodeState: lexerShortcodeState{
 			currLeftDelimItem:  tLeftDelimScNoMarkup,
 			currRightDelimItem: tRightDelimScNoMarkup,
-			openShortcodes:     make(map[string]bool),
+			openShortcodes:     make(map[unique.Handle[string]]bool),
 		},
 		items: make([]Item, 0, 5),
 	}

parser/pageparser/pagelexer_shortcode.go

@@ -13,15 +13,17 @@
 
 package pageparser
 
+import "unique"
+
 type lexerShortcodeState struct {
 	currLeftDelimItem  ItemType
 	currRightDelimItem ItemType
 	isInline           bool
-	currShortcodeName  string          // is only set when a shortcode is in opened state
-	closingState       int             // > 0 = on its way to be closed
-	elementStepNum     int             // step number in element
-	paramElements      int             // number of elements (name + value = 2) found first
-	openShortcodes     map[string]bool // set of shortcodes in open state
+	currShortcodeName  string                         // is only set when a shortcode is in opened state
+	closingState       int                            // > 0 = on its way to be closed
+	elementStepNum     int                            // step number in element
+	paramElements      int                            // number of elements (name + value = 2) found first
+	openShortcodes     map[unique.Handle[string]]bool // set of shortcodes in open state
 }
 
 // Shortcode syntax
@@ -254,10 +256,10 @@ Loop:
 			}
 		default:
 			l.backup()
-			word := string(l.input[l.start:l.pos])
+			word := unique.Make(string(l.input[l.start:l.pos]))
 			if l.closingState > 0 {
 				if !l.openShortcodes[word] {
-					return l.errorf("closing tag for shortcode '%s' does not match start tag", word)
+					return l.errorf("closing tag for shortcode '%s' does not match start tag", word.Value())
 				}
 				l.openShortcodes[word] = false
 				lookForEnd = true
@@ -266,7 +268,7 @@ Loop:
 			}
 
 			l.closingState = 0
-			l.currShortcodeName = word
+			l.currShortcodeName = word.Value()
 			l.elementStepNum++
 			if l.isInline {
 				l.emit(tScNameInline)