Translate missing Spanish sections in c-api/stable.po

[aislamg2]

Two-tier C API structure description - Explanation of the two stability levels Unstable API reference - Description of the unstable API tier with PyUnstable prefix Limited API reference - Description of the limited API tier with Py_LIMITED_API macro Transitional sentence - "These are discussed in more detail below" Unstable C API section title - Header for the unstable API section PyUnstable behavior documentation - How the PyUnstable prefix APIs change across versions Unstable API target audience - Intended for specialized low-level tools like debuggers Developer expectations - Projects using this API must follow CPython development closely Stable ABI section title - Header for the stable ABI section Stable ABI introduction - Python's stable ABI definition and compatibility promise