feat!: add Rego Virtual Machine (RVM) implementation (#495)

* feat!: add Rego Virtual Machine (RVM) implementation

This commit introduces a register-based virtual machine for executing Rego
policies with bytecode-style instructions. Unlike the existing tree-walking
interpreter, the RVM compiles policies into instruction sequences that operate
on virtual registers, offering better performance and optimization potential.

Core Components:

Instruction Set Architecture:
- Define instruction types for data operations, control flow, and builtins
- Implement instruction parameter encoding and display formatting
- Add instruction parser with comprehensive test coverage

Virtual Machine Engine:
- Register-based execution model with program counter management
- Loop execution supporting iterators, comprehensions, and quantifiers
- Function call handling with argument evaluation and context management
- Rule evaluation with default value resolution and virtual data support
- Arithmetic and comparison operation implementations

Program Representation:
- Program listing builder with instruction sequencing
- Rule tree construction for organizing policy rules
- Binary and JSON serialization for compiled programs
- Recompilation support for program modification

Testing Infrastructure:
- Extensive YAML test suites covering all VM features
- Rust unit tests for VM execution and instruction parsing
- Test suites for loops, comprehensions, builtins, and control flow

BREAKING CHANGE: Introduces new VM execution path alongside interpreter

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

* docs: add detailed RVM architecture references

Introduce architecture.md explaining program artifacts, serialization, and runtime subsystems.
Document the full opcode catalog in instruction-set.md, including operands, parameter tables, and outcomes.
Walk through execution flow, stacks, and operational guidance in vm-runtime.md, tying the runtime to the new architecture docs.

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

---------

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

tests/rvm/vm/suites/loop_invalid_iteration.yaml

@@ -0,0 +1,43 @@
+# Loop Invalid Iteration Test Suite
+# Asserts loop error paths and instruction limit behavior.
+
+cases:
+  - note: loop_start_on_scalar
+    description: LoopStart over scalar treats collection as empty and leaves result false
+    literals:
+      - 1
+    instruction_params:
+      loop_params:
+        - mode: "ForEach"
+          collection: 0
+          key_reg: 1
+          value_reg: 2
+          result_reg: 3
+          body_start: 2
+          loop_end: 2
+    instructions:
+      - "Load { dest: 0, literal_idx: 0 }"
+      - "LoopStart { params_index: 0 }"
+      - "Return { value: 3 }"
+    want_result: false
+
+  - note: instruction_limit_exceeded
+    description: VM stops once max instruction limit reached
+    literals:
+      - [1, 2]
+    instruction_params:
+      loop_params:
+        - mode: "ForEach"
+          collection: 0
+          key_reg: 1
+          value_reg: 2
+          result_reg: 3
+          body_start: 2
+          loop_end: 4
+    max_instructions: 3
+    instructions:
+      - "Load { dest: 0, literal_idx: 0 }"
+      - "LoopStart { params_index: 0 }"
+      - "LoopNext { body_start: 2, loop_end: 4 }"
+      - "Return { value: 3 }"
+    want_error: "exceeded maximum instruction limit"