feat: add pexpect and yaml modules with jinja from-import support

Add new pexpect module for process spawning and interaction, including Spawn class with expect, sendline, and timeout handling. Introduce yaml module for YAML parsing with support for nested structures, lists, and data types. Extend jinja template engine with brace tokenization and FromImportNode for macro imports across templates. Register all new foreign functions in modules.c and include generated demo scripts.

test/yaml/comments.wren

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+// retoor <retoor@molodetz.nl>
+
+import "yaml" for Yaml
+
+var yaml = "
+# This is a comment
+name: test
+# Another comment
+value: 123
+"
+
+var data = Yaml.parse(yaml)
+System.print(data["name"]) // expect: test
+System.print(data["value"]) // expect: 123
+
+var inlineComment = "name: test # inline comment"
+var data2 = Yaml.parse(inlineComment)
+System.print(data2["name"]) // expect: test

test/yaml/complex.wren

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+// retoor <retoor@molodetz.nl>
+
+import "yaml" for Yaml
+
+var yaml = "
+sections:
+  - title: Getting Started
+    pages:
+      - file: index
+        title: Overview
+      - file: installation
+        title: Installation
+  - title: API Reference
+    pages:
+      - file: json
+        title: json
+"
+
+var nav = Yaml.parse(yaml)
+System.print(nav["sections"][0]["title"]) // expect: Getting Started
+System.print(nav["sections"][0]["pages"][0]["file"]) // expect: index
+System.print(nav["sections"][0]["pages"][0]["title"]) // expect: Overview
+System.print(nav["sections"][0]["pages"][1]["file"]) // expect: installation
+System.print(nav["sections"][1]["title"]) // expect: API Reference
+System.print(nav["sections"][1]["pages"][0]["file"]) // expect: json

test/yaml/error_invalid.wren

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+// retoor <retoor@molodetz.nl>
+
+import "yaml" for Yaml
+
+var empty = Yaml.parse("")
+System.print(empty) // expect: null
+
+var nullInput = Yaml.parse(null)
+System.print(nullInput) // expect: null
+
+var whitespace = Yaml.parse("   \n   \n   ")
+System.print(whitespace) // expect: null

test/yaml/lists.wren

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+// retoor <retoor@molodetz.nl>
+
+import "yaml" for Yaml
+
+var yaml = "items:\n  - first\n  - second\n  - third"
+var data = Yaml.parse(yaml)
+System.print(data["items"][0]) // expect: first
+System.print(data["items"][1]) // expect: second
+System.print(data["items"][2]) // expect: third
+System.print(data["items"].count) // expect: 3
+
+var simple = "- one\n- two\n- three"
+var list = Yaml.parse(simple)
+System.print(list[0]) // expect: one
+System.print(list[1]) // expect: two
+System.print(list.count) // expect: 3
+
+var numbers = "- 1\n- 2\n- 3"
+var numList = Yaml.parse(numbers)
+System.print(numList[0]) // expect: 1
+System.print(numList[1]) // expect: 2

test/yaml/nested.wren

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+// retoor <retoor@molodetz.nl>
+
+import "yaml" for Yaml
+
+var yaml = "server:\n  host: localhost\n  port: 8080"
+var config = Yaml.parse(yaml)
+System.print(config["server"]["host"]) // expect: localhost
+System.print(config["server"]["port"]) // expect: 8080
+
+var deep = "
+level1:
+  level2:
+    level3:
+      value: deep
+"
+var deepConfig = Yaml.parse(deep)
+System.print(deepConfig["level1"]["level2"]["level3"]["value"]) // expect: deep

test/yaml/parse.wren

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+// retoor <retoor@molodetz.nl>
+
+import "yaml" for Yaml
+
+var simple = Yaml.parse("name: test")
+System.print(simple["name"]) // expect: test
+
+var num = Yaml.parse("count: 42")
+System.print(num["count"]) // expect: 42
+
+var float = Yaml.parse("value: 3.14")
+System.print(float["value"]) // expect: 3.14
+
+var bool = Yaml.parse("active: true")
+System.print(bool["active"]) // expect: true
+
+var boolFalse = Yaml.parse("active: false")
+System.print(boolFalse["active"]) // expect: false
+
+var nullVal = Yaml.parse("value: null")
+System.print(nullVal["value"]) // expect: null
+
+var quoted = Yaml.parse("name: \"hello world\"")
+System.print(quoted["name"]) // expect: hello world
+
+var singleQuoted = Yaml.parse("name: 'hello world'")
+System.print(singleQuoted["name"]) // expect: hello world

test/yaml/stringify.wren

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+// retoor <retoor@molodetz.nl>
+
+import "yaml" for Yaml
+
+var simple = {"name": "test", "value": 42}
+var str = Yaml.stringify(simple)
+System.print(str.contains("name: test")) // expect: true
+System.print(str.contains("value: 42")) // expect: true
+
+var withList = {"items": ["one", "two", "three"]}
+var listStr = Yaml.stringify(withList)
+System.print(listStr.contains("items:")) // expect: true
+System.print(listStr.contains("- one")) // expect: true
+System.print(listStr.contains("- two")) // expect: true
+
+var nested = {"server": {"host": "localhost", "port": 8080}}
+var nestedStr = Yaml.stringify(nested)
+System.print(nestedStr.contains("server:")) // expect: true
+System.print(nestedStr.contains("host: localhost")) // expect: true
+
+System.print(Yaml.stringify(null)) // expect: null
+System.print(Yaml.stringify(true)) // expect: true
+System.print(Yaml.stringify(false)) // expect: false
+System.print(Yaml.stringify(42)) // expect: 42
+System.print(Yaml.stringify("hello")) // expect: hello