Performance issue at WAF compilation

[racheedevel]

Description

Quadratic complexity when compiling a new WAF, since each rule goes through RuleGroup.Add, which calls RuleGroup.FindById, which does a full pass through the existing rules, which at 100 000 rules takes ~30s to compile.

Steps to reproduce

Not a user-facing issue, but this performance benchmark helps see the complexity is quadratic:

// internal/corazawaf/rulegroup_bench_test.go
package corazawaf
import (
	"strconv"
	"testing"
)

func BenchmarkRuleGroupAdd(b *testing.B) {
	for _, n := range []int{1_000, 10_000, 100_000} {
		b.Run(strconv.Itoa(n), func(b *testing.B) {
			for i := 0; i < b.N; i++ {
				rg := NewRuleGroup()
				for id := 1; id <= n; id++ {
					if err := rg.Add(newTestRule(id)); err != nil {
						b.Fatal(err)
					}
				}
			}
		})
	}
}

Expected result

Expectation would be that linear or more-or-less linear compilation times are visible, something like

Rules	Compile
1,000	8 ms
10,000	80 ms - 160 ms
100,000	800 ms - 1600ms

Actual result

Rules	Compile
1,000	8 ms
10,000	241 ms
100,000	30,616 ms

The 100k ruleset takes 127x as much time as the 10k ruleset.

Will throw in my PR as well to address it! :)