docs: Add optimizer documentation

src/Neo.Compiler.CSharp/Optimizer/README.md

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+# Neo Smart Contract Optimizer
+
+The Neo Compiler includes a powerful bytecode optimizer that reduces contract size and gas consumption. This document describes the available optimization strategies.
+
+## Overview
+
+The optimizer runs after initial compilation and applies various strategies to improve the generated NeoVM bytecode. Each strategy can be enabled/disabled independently.
+
+## Optimization Strategies
+
+### 1. Peephole Optimization (`Peephole.cs`)
+
+**Purpose**: Pattern-based local optimizations that replace inefficient instruction sequences with more efficient equivalents.
+
+**Key Optimizations**:
+- **Dead code elimination**: Removes unreachable instructions
+- **Redundant operation removal**: Eliminates unnecessary DUP/DROP pairs
+- **Constant folding**: Pre-computes constant expressions at compile time
+- **Instruction simplification**: Replaces complex sequences with simpler equivalents
+
+**Example**:
+```
+Before: PUSH1 PUSH2 ADD
+After:  PUSH3
+```
+
+### 2. Jump Compression (`JumpCompresser.cs`)
+
+**Purpose**: Optimizes jump instructions by using shorter jump variants when possible.
+
+**Key Optimizations**:
+- Converts `JMP_L` (5 bytes) to `JMP` (2 bytes) when target is within range
+- Removes redundant jumps (jump to next instruction)
+- Chains consecutive jumps
+
+**Benefits**: Significant size reduction in contracts with many branches.
+
+### 3. Reachability Analysis (`Reachability.cs`)
+
+**Purpose**: Identifies and removes unreachable code paths.
+
+**Key Optimizations**:
+- Detects dead code after unconditional jumps/returns
+- Removes unused exception handlers
+- Eliminates unreachable branches
+
+### 4. Miscellaneous Optimizations (`Miscellaneous.cs`)
+
+**Purpose**: Various small optimizations that don't fit other categories.
+
+**Key Optimizations**:
+- NOP removal
+- Redundant type conversion elimination
+- Stack operation simplification
+
+## Usage
+
+Optimization is enabled by default. Control it via compiler options:
+
+```bash
+# Full optimization (default)
+nccs MyContract.csproj
+
+# Disable optimization
+nccs MyContract.csproj --no-optimize
+
+# Specific optimization level
+nccs MyContract.csproj --optimize basic
+```
+
+## Architecture
+
+```
+Optimizer/
+├── Analysers/           # Code analysis utilities
+│   ├── InstructionCoverage.cs
+│   └── TryCatchFinallyCoverage.cs
+├── AssetBuilder/        # Output generation
+│   ├── DebugInfoBuilder.cs
+│   └── OptimizedScriptBuilder.cs
+├── Strategies/          # Optimization strategies
+│   ├── Peephole.cs
+│   ├── JumpCompresser.cs
+│   ├── Reachability.cs
+│   └── Miscellaneous.cs
+├── BasicOptimizer.cs    # Main optimizer entry point
+└── DumpNef.cs           # NEF file utilities
+```
+
+## Adding New Strategies
+
+1. Create a new class in `Strategies/`
+2. Implement the optimization logic
+3. Add the `[Strategy]` attribute
+4. Register in `BasicOptimizer.cs`
+
+## Performance Impact
+
+Typical optimization results:
+- **Size reduction**: 10-30% smaller bytecode
+- **Gas savings**: 5-20% lower execution cost
+- **Compilation time**: Minimal overhead (~100ms)
+
+## See Also
+
+- [Neo Compiler Documentation](../../docs/)
+- [NeoVM Instruction Reference](https://docs.neo.org/docs/n3/reference/neo_vm)