Refactor: major codebase update and improvements

Algorithm & Flowchart.md

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+## DNS Server Algorithm
+
+**1. Server Initialization**
+
+```rust
+1.1 Load configuration from environment variables
+1.2 Initialize logging system
+1.3 Create SQLite database connection
+1.4 Initialize cache with NS records
+1.5 Start periodic cache cleanup task
+1.6 Bind UDP and TCP sockets on specified port
+```
+
+**2. Query Handling Flow**
+
+```
+                    Start
+                      │
+                      ▼
+               Receive DNS Query
+                      │
+                      ▼
+            Parse Query Header/Question
+                      │
+                      ▼
+          Check Cache for Domain Record
+              ┌───────┴───────┐
+              ▼               ▼
+         Cache Hit      Cache Miss
+              │               │
+              ▼               ▼
+       Build Response    Query Database
+                              │
+                              ▼
+                   Check Authoritative Flag
+                      ┌────────┴────────┐
+                      ▼                 ▼
+                Record Found      Record Not Found
+                      │                 │
+                      ▼                 ▼
+               Build Response    Forward to Resolvers
+                      │                 │
+                      ▼                 ▼
+                  Add DNSSEC           ▼
+                 Signatures       Receive Forwarded Response
+                      │                 │
+                      ▼                 ▼
+               Send Response to Client
+                      │
+                      ▼
+                     End
+```
+
+**3. DNSSEC Signing Process**
+
+```rust
+3.1 Load DNSSEC key from configured file
+3.2 For each relevant DNS record:
+    3.2.1 Generate RRSIG record
+    3.2.2 Encode signature using Base64
+    3.2.3 Calculate key tag and signature expiration
+3.3 Add RRSIG records to DNS response
+3.4 Include DNSKEY records in authority section
+```
+
+**4. Response Generation Logic**
+
+```
+4.1 Create response header with:
+    - Original query ID
+    - QR flag set to response
+    - Authoritative Answer flag
+    - Appropriate response code (NOERROR/NXDOMAIN)
+    
+4.2 Add original question section
+
+4.3 Populate answer section with:
+    - Resource records from cache/database
+    - TTL values from configuration
+    
+4.4 Add authority section with:
+    - NS records
+    - DS records for DNSSEC
+    
+4.5 Include additional section with:
+    - A records for NS names
+    - DNSKEY records when applicable
+```
+
+
+## Key Data Flow Components
+
+| Component | Purpose | Implementation Details |
+| :-- | :-- | :-- |
+| `DnsCache` | Response caching | Mutex-protected HashMap with TTL |
+| `ServerConfig` | Runtime configuration | Environment variables parsing |
+| `rusqlite` | Persistent storage | SQLite database with DNS records |
+| `tokio` | Async I/O handling | UDP/TCP listeners with task spawning |
+| `DNSSEC` | Response signing | RSA-SHA256 with preloaded keys |
+
+## Error Handling Strategy
+
+```rust
+- Use custom DnsError enum with thiserror crate
+- Graceful shutdown on SIGINT
+- Automatic cache cleanup every 5 minutes
+- Fallback to forwarding when local resolution fails
+- Comprehensive logging at all stages
+```
+
+The server implements RFC 1035 (DNS) and RFC 4034 (DNSSEC) specifications with a focus on:
+
+1. Async I/O using Tokio runtime
+2. Thread-safe caching with atomic reference counting
+3. Configurable forwarding and fallback mechanisms
+4. DNSSEC signing capability for authoritative responses
+5. SQLite-based record storage with schema versioning
+
+<div style="text-align: center">⁂</div>