Add cache for common package queries (#22491)

This adds a cache for common package queries in `GetPackageDescriptor`.
Code which needs to process a list of packages benefits from this
change. This skips 350 queries in the package integration tests for
example.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/cache/ephemeral.go

@@ -0,0 +1,90 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package cache
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/util"
+)
+
+// EphemeralCache is a cache that can be used to store data in a request level context
+// This is useful for caching data that is expensive to calculate and is likely to be
+// used multiple times in a request.
+type EphemeralCache struct {
+	data          map[any]map[any]any
+	lock          sync.RWMutex
+	created       time.Time
+	checkLifeTime time.Duration
+}
+
+var timeNow = time.Now
+
+func NewEphemeralCache(checkLifeTime ...time.Duration) *EphemeralCache {
+	return &EphemeralCache{
+		data:          make(map[any]map[any]any),
+		created:       timeNow(),
+		checkLifeTime: util.OptionalArg(checkLifeTime, 0),
+	}
+}
+
+func (cc *EphemeralCache) checkExceededLifeTime(tp, key any) bool {
+	if cc.checkLifeTime > 0 && timeNow().Sub(cc.created) > cc.checkLifeTime {
+		log.Warn("EphemeralCache is expired, is highly likely to be abused for long-life tasks: %v, %v", tp, key)
+		return true
+	}
+	return false
+}
+
+func (cc *EphemeralCache) Get(tp, key any) (any, bool) {
+	if cc.checkExceededLifeTime(tp, key) {
+		return nil, false
+	}
+	cc.lock.RLock()
+	defer cc.lock.RUnlock()
+	ret, ok := cc.data[tp][key]
+	return ret, ok
+}
+
+func (cc *EphemeralCache) Put(tp, key, value any) {
+	if cc.checkExceededLifeTime(tp, key) {
+		return
+	}
+
+	cc.lock.Lock()
+	defer cc.lock.Unlock()
+
+	d := cc.data[tp]
+	if d == nil {
+		d = make(map[any]any)
+		cc.data[tp] = d
+	}
+	d[key] = value
+}
+
+func (cc *EphemeralCache) Delete(tp, key any) {
+	if cc.checkExceededLifeTime(tp, key) {
+		return
+	}
+
+	cc.lock.Lock()
+	defer cc.lock.Unlock()
+	delete(cc.data[tp], key)
+}
+
+func GetWithEphemeralCache[T, K any](ctx context.Context, c *EphemeralCache, groupKey string, targetKey K, f func(context.Context, K) (T, error)) (T, error) {
+	v, has := c.Get(groupKey, targetKey)
+	if vv, ok := v.(T); has && ok {
+		return vv, nil
+	}
+	t, err := f(ctx, targetKey)
+	if err != nil {
+		return t, err
+	}
+	c.Put(groupKey, targetKey, t)
+	return t, nil
+}