[performance] overhaul struct (+ result) caching library for simplicity, performance and multiple-result lookups (#2535)

* rewrite cache library as codeberg.org/gruf/go-structr, implement in gotosocial

* use actual go-structr release version (not just commit hash)

* revert go toolchain changes (damn you go for auto changing this)

* fix go mod woes

* ensure %w is used in calls to errs.Appendf()

* fix error checking

* fix possible panic

* remove unnecessary start/stop functions, move to main Cache{} struct, add note regarding which caches require start/stop

* fix copy-paste artifact... 😇

* fix all comment copy-paste artifacts

* remove dropID() function, now we can just use slices.DeleteFunc()

* use util.Deduplicate() instead of collate(), move collate to util

* move orderByIDs() to util package and "generify"

* add a util.DeleteIf() function, use this to delete entries on failed population

* use slices.DeleteFunc() instead of util.DeleteIf() (i had the logic mixed up in my head somehow lol)

* add note about how collate differs from deduplicate

vendor/codeberg.org/gruf/go-structr/list.go

@@ -0,0 +1,130 @@
+package structr
+
+// elem represents an element
+// in a doubly-linked list.
+type elem[T any] struct {
+	next  *elem[T]
+	prev  *elem[T]
+	Value T
+}
+
+// list implements a doubly-linked list, where:
+// - head = index 0   (i.e. the front)
+// - tail = index n-1 (i.e. the back)
+type list[T any] struct {
+	head *elem[T]
+	tail *elem[T]
+	len  int
+}
+
+func list_acquire[T any](c *Cache[T]) *list[*result[T]] {
+	var l *list[*result[T]]
+
+	if len(c.llsPool) == 0 {
+		// Allocate new list.
+		l = new(list[*result[T]])
+	} else {
+		// Pop list from pool slice.
+		l = c.llsPool[len(c.llsPool)-1]
+		c.llsPool = c.llsPool[:len(c.llsPool)-1]
+	}
+
+	return l
+}
+
+func list_release[T any](c *Cache[T], l *list[*result[T]]) {
+	// Reset list.
+	l.head = nil
+	l.tail = nil
+	l.len = 0
+
+	// Release list to memory pool.
+	c.llsPool = append(c.llsPool, l)
+}
+
+// pushFront pushes new 'elem' to front of list.
+func (l *list[T]) pushFront(elem *elem[T]) {
+	if l.len == 0 {
+		// Set new tail + head
+		l.head = elem
+		l.tail = elem
+
+		// Link elem to itself
+		elem.next = elem
+		elem.prev = elem
+	} else {
+		oldHead := l.head
+
+		// Link to old head
+		elem.next = oldHead
+		oldHead.prev = elem
+
+		// Link up to tail
+		elem.prev = l.tail
+		l.tail.next = elem
+
+		// Set new head
+		l.head = elem
+	}
+
+	// Incr count
+	l.len++
+}
+
+// moveFront calls remove() on elem, followed by pushFront().
+func (l *list[T]) moveFront(elem *elem[T]) {
+	l.remove(elem)
+	l.pushFront(elem)
+}
+
+// remove removes the 'elem' from the list.
+func (l *list[T]) remove(elem *elem[T]) {
+	if l.len <= 1 {
+		// Drop elem's links
+		elem.next = nil
+		elem.prev = nil
+
+		// Only elem in list
+		l.head = nil
+		l.tail = nil
+		l.len = 0
+		return
+	}
+
+	// Get surrounding elems
+	next := elem.next
+	prev := elem.prev
+
+	// Relink chain
+	next.prev = prev
+	prev.next = next
+
+	switch elem {
+	// Set new head
+	case l.head:
+		l.head = next
+
+	// Set new tail
+	case l.tail:
+		l.tail = prev
+	}
+
+	// Drop elem's links
+	elem.next = nil
+	elem.prev = nil
+
+	// Decr count
+	l.len--
+}
+
+// rangefn ranges all the elements in the list, passing each to fn.
+func (l *list[T]) rangefn(fn func(*elem[T])) {
+	if fn == nil {
+		panic("nil fn")
+	}
+	elem := l.head
+	for i := 0; i < l.len; i++ {
+		fn(elem)
+		elem = elem.next
+	}
+}