Docs: Conceal private setup methods (Issue #816)

[PratapShashwat]

Motivation

This PR addresses Issue #816. The auto-generated documentation for `netpyne.sim` currently exposes several internal "plumbing" methods (e.g., `setNet`, `setNetParams`) that are intended to be called only by `initialize()`. Exposing these confuses users who might try to call them manually.

Changes

I have renamed the following internal methods in `netpyne/sim/setup.py` by adding a leading underscore (`_`), which causes Sphinx to exclude them from the public API docs:

• `setNet` → `_setNet`
• `setNetParams` → `_setNetParams`
• `setSimCfg` → `_setSimCfg`
• `createParallelContext` → `_createParallelContext`
• `setGlobals` → `_setGlobals`
• `setupRecordLFP` → `_setupRecordLFP`
• `setupRecordDipole` → `_setupRecordDipole`

Verification

• Internal Consistency: Updated all internal calls to these methods in `netpyne/sim/init.py`, `wrappers.py`, `load.py`, and `gather.py`.
• Safety Check: Verified via `grep` that these methods are not used in `tutorials/` or `examples/`.
• Docs Build: Built the documentation locally; confirmed these methods no longer appear in the "Package Reference" section.