Introduce a ScopedContext Class for Automatic Context Management

[pmqtt]

Description

Currently, context management in the parser relies on manual push and pop operations for the _context stack. This leads to repetitive code and increases the risk of inconsistencies.

Solution

Create a ScopedContext class that automatically pushes a context on creation and pops it on destruction.

Steps

Implement the ScopedContext class.
Replace existing push/pop calls with ScopedContext.
Example Usage

ScopedContext scoped_context(_context, {.context = "expression", .rule = RuleType::EXPRESSION});