Add RTL functions for arithmetic and comparisons

This commit introduces a new module `ast::rtl` to house the standard
runtime library functions for the language. It includes implementations
for arithmetic operators (+, -, *, /, //, %), logical operators (and,
or, xor, not), bitwise shifts (<<, >>), and comparison operators (=, <>,
<, >, <=, >=).

Additionally, a `date` function for parsing datetime strings has been
added. This enhances the language's capability to handle basic
mathematical and logical operations.
Add RTL functions for arithmetic and comparisons

This commit introduces the runtime library (RTL) functions for basic
arithmetic operations, logical/bitwise operations, and comparisons. It
also includes a `date` function for parsing datetime strings.
Integration tests have been updated to cover these new functionalities.

src/ast/rtl/datetime.rs

@@ -0,0 +1,25 @@
+use crate::ast::types::{Value, StaticType, Signature};
+use crate::ast::environment::Environment;
+use chrono::{NaiveDate, NaiveDateTime};
+
+pub fn register(env: &Environment) {
+    let date_ty = StaticType::Function(Box::new(Signature {
+        params: vec![StaticType::Text],
+        ret: StaticType::DateTime
+    }));
+    
+    env.register_native("date", date_ty, |args| {
+        if let Value::Text(s) = &args[0] {
+            // Try parse YYYY-MM-DD
+            if let Ok(dt) = NaiveDate::parse_from_str(s, "%Y-%m-%d") {
+                let ts = dt.and_hms_opt(0, 0, 0).unwrap().and_utc().timestamp_millis();
+                return Value::DateTime(ts);
+            }
+            // Try parse YYYY-MM-DD HH:MM:SS
+            if let Ok(dt) = NaiveDateTime::parse_from_str(s, "%Y-%m-%d %H:%M:%S") {
+                return Value::DateTime(dt.and_utc().timestamp_millis());
+            }
+        }
+        Value::Void
+    });
+}