feat: config loader, PR formatter, VS Code diagnostics, and SARIF/JSON CLI output

[Nimatstar]

Implements four assigned GasGuard features on one branch.

#592 — .gasguardrc config loader

Adds src/config/config.interface.ts and src/config/config-loader.ts: loads .gasguardrc, .gasguardrc.json, and .gasguardrc.yaml/.yml, supporting ignoreRules, includePaths, excludePaths, and severityThreshold, and falling back to defaults when no file is present. isPathExcluded() lets the scanner skip excluded paths during AST parsing. YAML is parsed by a tiny built-in reader for the flat config shape, so no new dependency is added.

#591 — GitHub PR comment formatter

Adds packages/formatters/src/github-pr-formatter.ts: renders diagnostics into a GitHub-flavored Markdown table (File, Line, Rule, Gas Impact, Suggested Fix), wraps large reports in a collapsible <details> block, and computes aggregate potential gas savings across the changeset.

#590 — VS Code inline diagnostics

Adds packages/vscode-extension/src/diagnostics.ts and extension.ts: binds a vscode.languages.createDiagnosticCollection('gasguard'), maps rule matches to vscode.Diagnostic ranges at Warning severity (so squiggly underlines appear in .sol/.rs files), and surfaces the estimated gas saving in the hover message.

#589 — CLI JSON and SARIF output

Adds apps/cli/src/formatters/sarif-formatter.ts (maps RuleMatch objects to SARIF v2.1.0) and apps/cli/src/commands/scan.ts with --format (text|json|sarif) and --output <file> handling, so results can feed GitHub code scanning and CI dashboards.

Unit tests are included for the config loader, PR formatter, and SARIF formatter.

closes #592
closes #591
closes #590
closes #589

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