fix(sub): convert far expiry dates to Jalali in constant time

gregorianToJalali walked the calendar one month at a time from a 2024
reference, so an expiry near the int64 limit (a node reports expiries
unchecked) cost seconds of CPU on every subscription fetch that renders
{{JALALI_EXPIRE_DATE}}. Jalali leap years repeat every 33 years, so
whole 33-year blocks are skipped before the walk.

internal/sub/remark_vars.go

@@ -423,6 +423,13 @@ func gregorianToJalali(gy, gm, gd int) (jy, jm, jd int) {
 	refJDN := 2460311
 	days := int64(jdn - refJDN)
 	jy, jm, jd = 1402, 10, 11
+	// Leap years follow y % 33, so whole 33-year blocks are skipped: a node-reported expiry
+	// can lie hundreds of millions of years away, and the walk below goes month by month.
+	const jalaliCycleDays = 33*365 + 8
+	if cycles := days / jalaliCycleDays; cycles != 0 {
+		jy += int(cycles) * 33
+		days -= cycles * jalaliCycleDays
+	}
 
 	// Walk forward
 	for days > 0 {

internal/sub/remark_vars_test.go

@@ -4,6 +4,7 @@ import (
 	"net/url"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/mhsanaei/3x-ui/v3/internal/database/model"
 	"github.com/mhsanaei/3x-ui/v3/internal/xray"
@@ -529,6 +530,8 @@ func TestGregorianToJalali(t *testing.T) {
 		{2024, 1, 1, 1402, 10, 11},
 		{2000, 3, 20, 1379, 1, 1},
 		{1979, 2, 11, 1357, 11, 22},
+		// 2124-01-01 lies three 33-year blocks and a year past the reference.
+		{2124, 1, 1, 1502, 10, 11},
 	}
 	for _, c := range cases {
 		jy, jm, jd := gregorianToJalali(c.gy, c.gm, c.gd)
@@ -539,6 +542,19 @@ func TestGregorianToJalali(t *testing.T) {
 	}
 }
 
+// A node reports the expiry the remark renders, so a date hundreds of millions of years
+// out must not walk the calendar month by month on every subscription fetch.
+func TestGregorianToJalaliFarDatesTakeConstantTime(t *testing.T) {
+	start := time.Now()
+	if jy, _, _ := gregorianToJalali(292000000, 1, 1); jy < 290000000 {
+		t.Fatalf("year 292000000 converted to Jalali year %d", jy)
+	}
+	_, _, _ = gregorianToJalali(-292000000, 1, 1)
+	if took := time.Since(start); took > 100*time.Millisecond {
+		t.Fatalf("converting far dates took %v", took)
+	}
+}
+
 func TestJalaliExpireDateLabel(t *testing.T) {
 	if got := jalaliExpireDateLabel(0); got != "" {
 		t.Errorf("jalaliExpireDateLabel(0) = %q, want empty", got)