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/python.rs

@@ -0,0 +1,40 @@
+use crate::patterns::{Pattern, Severity};
+
+pub const PATTERNS: &[Pattern] = &[
+  Pattern {
+    id: "eval_call",
+    description: "eval() on dynamic input",
+    query: "(call function: (identifier) @id (#eq? @id \"eval\")) @vuln",
+    severity: Severity::High,
+  },
+  Pattern {
+    id: "exec_call",
+    description: "exec(...) execution of dynamic code",
+    query: "(call function: (identifier) @id (#eq? @id \"exec\")) @vuln",
+    severity: Severity::High,
+  },
+  Pattern {
+    id: "pickle_load",
+    description: "pickle.load / loads – unsafe deserialization",
+    query: "(call function: (attribute attribute: (identifier) @attr (#match? @attr \"load(s)?\") object: (identifier) @pkg (#eq? @pkg \"pickle\"))) @vuln",
+    severity: Severity::High,
+  },
+  Pattern {
+    id: "subprocess_shell_true",
+    description: "subprocess.* with shell=True",
+    query: "(call function: (attribute object: (identifier) @pkg (#eq? @pkg \"subprocess\")) arguments: (argument_list . (keyword_argument name: (identifier) @k (#eq? @k \"shell\")) (true) @val)) @vuln",
+    severity: Severity::Medium,
+  },
+  Pattern {
+    id: "random_random",
+    description: "random.random() for security-sensitive randomness",
+    query: "(call function: (attribute attribute: (identifier) @attr (#eq? @attr \"random\") object: (identifier) @pkg (#eq? @pkg \"random\"))) @vuln",
+    severity: Severity::Low,
+  },
+  Pattern {
+    id: "sql_concat",
+    description: "SQL query built via f-string or +-concat",
+    query: "(call function: (attribute attribute: (identifier) @m (#match? @m \"execute|executemany\")) arguments: (argument_list (f_string) @fstr)) @vuln",
+    severity: Severity::Medium,
+  },
+];