fix(python-sdk): add robust input validation and timeout bounding to REST requests

[mozluk]

Motivation

This PR hardens the python-sdk repository by introducing comprehensive input validation bounds and explicit network request timeouts, as identified during the Pacific-Fi security audit[cite: 29]. Previously, decimal amounts, addresses, and leverage parameters lacked strict format and range checks, and outgoing REST requests lacked execution timeouts[cite: 29].

Modifications

• Shared Input Validation (common/validate.py, tests/test_validate.py):
  • Implemented strict decimal string parsing and exact base-unit conversion (to_base_units) to prevent floating-point precision loss and silent token rounding[cite: 29].
  • Added validation guards for leverage ranges (1–50x) and base58 Solana address lengths[cite: 29].
  • Added and executed a comprehensive unit test suite covering validation logic[cite: 29].
• Outbound Request Bounding (rest/*):
  • Enforced explicit execution timeouts on all requests.get and requests.post calls to prevent hanging connections[cite: 29].
  • Migrated query string arguments to safe parameter passing (params=)[cite: 29].

Checklist

• Format your code according to the Contributor Guide.
• Add unit tests as outlined in the Contributor Guide.
• Update documentation as needed, including docstrings or example tutorials.