feat: implement Random and Time built-in effects

Add Random and Time effects for random number generation and
time-based operations. These effects can be used in any
effectful code block.

Random effect operations:
- Random.int(min, max) - random integer in range [min, max]
- Random.float() - random float in range [0.0, 1.0)
- Random.bool() - random boolean

Time effect operations:
- Time.now() - current Unix timestamp in milliseconds
- Time.sleep(ms) - sleep for specified milliseconds

Changes:
- Add rand crate dependency
- Add Random and Time effect definitions to types.rs
- Add effects to built-in effects list in typechecker
- Implement effect handlers in interpreter
- Add 4 new tests for Random and Time effects
- Add examples/random.lux demonstrating usage

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Cargo.lock

@@ -127,6 +127,17 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ff2abc00be7fca6ebc474524697ae276ad847ad0a6b3faa4bcb027e9a4614ad0"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.4.1"
@@ -358,6 +369,7 @@ version = "0.1.0"
 dependencies = [
  "lsp-server",
  "lsp-types",
+ "rand",
  "rustyline",
  "serde",
  "serde_json",
@@ -413,6 +425,15 @@ dependencies = [
  "zerovec",
 ]
 
+[[package]]
+name = "ppv-lite86"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85eae3c4ed2f50dcfe72643da4befc30deadb458a9b590d720cde2f2b1e97da9"
+dependencies = [
+ "zerocopy",
+]
+
 [[package]]
 name = "prettyplease"
 version = "0.2.37"
@@ -457,6 +478,36 @@ dependencies = [
  "nibble_vec",
 ]
 
+[[package]]
+name = "rand"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
+dependencies = [
+ "libc",
+ "rand_chacha",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
+dependencies = [
+ "getrandom 0.2.17",
+]
+
 [[package]]
 name = "rustix"
 version = "1.1.3"
@@ -593,7 +644,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0136791f7c95b1f6dd99f9cc786b91bb81c3800b639b3478e561ddb7be95e5f1"
 dependencies = [
  "fastrand",
- "getrandom",
+ "getrandom 0.4.1",
  "once_cell",
  "rustix",
  "windows-sys 0.61.2",
@@ -678,6 +729,12 @@ version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "06abde3611657adf66d383f00b093d7faecc7fa57071cce2578660c9f1010821"
 
+[[package]]
+name = "wasi"
+version = "0.11.1+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ccf3ec651a847eb01de73ccad15eb7d99f80485de043efb2f370cd654f4ea44b"
+
 [[package]]
 name = "wasip2"
 version = "1.0.2+wasi-0.2.9"
@@ -944,6 +1001,26 @@ dependencies = [
  "synstructure",
 ]
 
+[[package]]
+name = "zerocopy"
+version = "0.8.39"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "db6d35d663eadb6c932438e763b262fe1a70987f9ae936e60158176d710cae4a"
+dependencies = [
+ "zerocopy-derive",
+]
+
+[[package]]
+name = "zerocopy-derive"
+version = "0.8.39"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4122cd3169e94605190e77839c9a40d40ed048d305bfdc146e7df40ab0f3e517"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "zerofrom"
 version = "0.1.6"