Add multi-language AST-pattern scanning support

- Introduced `patterns` module with language-specific vulnerability patterns.
- Added `query_cache` utility for caching compiled queries.
- Expanded `scan.rs` to support scanning multiple languages dynamically.
- Updated `Cargo.toml` with additional tree-sitter dependencies.
- Added severity filtering to `ScannerConfig` for better configuration.

src/patterns/go.rs

@@ -0,0 +1,34 @@
+use crate::patterns::{Pattern, Severity};
+
+pub const PATTERNS: &[Pattern] = &[
+  Pattern {
+    id: "exec_command",
+    description: "os/exec Command construction",
+    query: "(call_expression function: (selector_expression field: (field_identifier) @f (#eq? @f \"Command\"))) @vuln",
+    severity: Severity::Medium,
+  },
+  Pattern {
+    id: "http_insecure_tls",
+    description: "&http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: true}}",
+    query: "(composite_literal type: (selector_expression field: (field_identifier) @t (#eq? @t \"Transport\")) body: (literal_value (keyed_element key: (identifier) @k (#eq? @k \"TLSClientConfig\") value: (composite_literal body: (literal_value (keyed_element key: (identifier) @ik (#eq? @ik \"InsecureSkipVerify\") value: (true)))))) @vuln",
+    severity: Severity::High,
+  },
+  Pattern {
+    id: "unsafe_pointer",
+    description: "Use of unsafe.Pointer",
+    query: "(qualified_type type: (selector_expression field: (field_identifier) @f (#eq? @f \"Pointer\"))) @vuln",
+    severity: Severity::High,
+  },
+  Pattern {
+    id: "md5_sha1",
+    description: "crypto/md5 or crypto/sha1 usage",
+    query: "(call_expression function: (selector_expression object: (identifier) @pkg (#match? @pkg \"md5|sha1\"))) @vuln",
+    severity: Severity::Medium,
+  },
+  Pattern {
+    id: "hardcoded_secret",
+    description: "Hard-coded string that looks like an API key/token",
+    query: "(interpreted_string_literal) @s (#match? @s \"(?i)(api|secret|token|password)[=:]?[ \\t]*[A-Za-z0-9_\\-]{8,}\")",
+    severity: Severity::Low,
+  },
+];