Improve JSON pretty printing in generated snippets

[Xvvln]

Closes #1555

Summary

This PR improves generated snippets for Python Requests and JavaScript Fetch by pretty-printing JSON responses when possible, while preserving a plain-text fallback for non-JSON responses.

Changes

• Python Requests snippets now import json and try json.dumps(response.json(), indent=4) before falling back to response.text
• JavaScript Fetch snippets now try JSON.parse(body) and log JSON.stringify(..., null, 2) before falling back to the raw body
• Updated codegen tests for both generators

Validation

• flutter test --no-pub test/codegen/python_requests_codegen_test.dart ✅
• flutter test --no-pub test/codegen/js_fetch_codegen_test.dart ✅

[Copilot]

Pull request overview

This PR enhances the Python Requests and JavaScript Fetch code generators to pretty-print JSON responses when possible, falling back to plain-text output when the response body is not valid JSON (closes #1555).

Changes:

• Python Requests snippets now import json and pretty-print response.json() with indent=4, falling back to response.text on JSON decode failure.
• JavaScript Fetch snippets now attempt to parse the response body as JSON and log a pretty-printed JSON.stringify(..., null, 2), falling back to the raw body.
• Updated generator tests to match the new output patterns.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
lib/codegen/python/requests.dart	Adds JSON pretty-printing with a try/except fallback in the generated Python snippet.
lib/codegen/js/fetch.dart	Adds JSON parse + pretty-print fallback logic to generated Fetch snippets.
test/codegen/python_requests_codegen_test.dart	Updates expected Python snippets to include import json and pretty-print/fallback behavior.
test/codegen/js_fetch_codegen_test.dart	Updates expected Fetch snippets to include JSON pretty-print/fallback behavior.

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[Copilot]

Using an async callback inside .then(...) introduces an async/await requirement for the generated snippet (ES2017). Since the previous version used a plain promise chain, consider keeping return res.text() and moving the JSON.parse/pretty-print into the next .then(body => ...) to preserve compatibility and avoid mixing async/await with .then() here.

[Copilot]

The generated snippet uses optional catch binding (catch { ... }), which is not supported in some older JS runtimes. To maximize snippet compatibility, use catch (e) { ... } even if e is unused.

Suggested change

	} catch {
	} catch (e) {