feat: add onSuccess and onFailure lifecycle hooks for telemetry

[AryanSharma48]

Description

Resolves a part of #7

This PR implements the onSuccess and onFailure lifecycle event hooks across both TypeScript (smooth-api-ts) and Python (smooth-api-py) clients, providing end-to-end request observability and telemetry integration (Datadog, Prometheus, OpenTelemetry).

Key Features & Design Choices:

• onSuccess:
  • Only clean HTTP 2xx completions trigger onSuccess.
  • Context includes url, domain, attempts taken to succeed, durationMs (or .duration_ms / .duration), status, and response.
• onFailure:
  • Terminal HTTP errors (status >= 400), exhausted retries, unhandled exceptions, and CircuitOpenError trigger onFailure.
  • Context includes url, domain, attempts, durationMs, error, status, response, and isCircuitOpen / is_circuit_open.
• Fail-Safe Execution:
  • User exceptions inside hook callbacks are safely caught and logged via safeInvoke / _safe_invoke, ensuring client requests never crash due to telemetry bugs.
• Python Parity:
  • Supports both snake_case (on_success, on_failure) and camelCase (onSuccess, onFailure) configuration aliases.
  • Automatically extracts target URLs from request arguments, response objects, or error contexts.

Affected Packages:

• packages/smooth-api-ts
• packages/smooth-api-py
• Root README.md

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Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation/Website update (changes to READMEs, examples, inline comments, or the documentation website)

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Checklist

Design & Parity

• If this introduces a new configuration option or public API, I have implemented equivalent options/behavior in both TypeScript and Python packages.
• The core packages remain dependency-free (no new external runtime dependencies added).
• I have updated the relevant package-specific README.md or general documentation where necessary.
• If applicable, I have updated the examples or website to reflect these changes.

Quality & Testing

• I started the sandbox Express server (cd sandbox && npm install && npm start) in a separate terminal before running the tests.
• TypeScript Package: I have run the TypeScript tests (npm install && npm run build && npm test inside packages/smooth-api-ts) and all tests passed (51/51 passing).
• Python Package: I have run the Python tests (pip install -e ".[dev]" && pytest inside packages/smooth-api-py) and all tests passed (51/51 passing, 0 ruff lint errors).
• I have added new tests to cover my changes.
• I have commented my code, particularly in hard-to-understand areas, and updated JSDoc/docstrings.