some preparation for reccurence expansion

Cargo.lock

@@ -2894,6 +2894,19 @@ dependencies = [
  "windows-sys 0.59.0",
 ]
 
+[[package]]
+name = "rrule"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "720acfb4980b9d8a6a430f6d7a11933e701ebbeba5eee39cc9d8c5f932aaff74"
+dependencies = [
+ "chrono",
+ "chrono-tz",
+ "log",
+ "regex",
+ "thiserror 2.0.12",
+]
+
 [[package]]
 name = "rsa"
 version = "0.9.8"
@@ -3191,6 +3204,7 @@ dependencies = [
  "ical",
  "lazy_static",
  "regex",
+ "rrule",
  "rustical_xml",
  "strum",
  "strum_macros",
@@ -3227,6 +3241,7 @@ dependencies = [
  "lazy_static",
  "rand 0.8.5",
  "regex",
+ "rrule",
  "rstest",
  "rstest_reuse",
  "rustical_dav",