Add momentum_aperture method to Line class

[gbrogginess]

Description

This PR introduces a new method:

line.momentum_aperture(...)

to compute the local momentum aperture (also referred to as local momentum acceptance, LMA) along a beamline by tracking particles with varying momentum offsets from selected elements.

The method evaluates, for each selected longitudinal location, the maximum stable negative and positive momentum deviations (δ) over a configurable number of turns.

For each location, particles are generated around the local closed orbit, a grid of momentum offsets is applied, and particles are tracked to determine the largest surviving negative and positive δ values.

The output is returned as an xt.Table indexed by longitudinal position s.

This feature is important because the local momentum acceptance is a key quantity for Touschek and quantum lifetime studies and their optimization.

A dedicated test suite covering this new functionality has been added.

Checklist

Mandatory:

• I have added tests to cover my changes
• All the tests are passing, including my new ones
• I described my changes in this PR description

Optional:

• The code I wrote follows good style practices (see PEP 8 and PEP 20).
• I have updated the docs in relation to my changes, if applicable
• I have tested also GPU contexts