Xtrack version 0.57.2

Changes:

• Introduce Line.get_ibs_growth_rates(...)
• Introduce Line._insert_thick_elements_at_s(...)
• Replace _allow_backtrack with _allow_loss_refinement
• Add s_tol in element insertion methods.
• Better initialization of io_buffer

Full Changelog: v0.57.1...v0.57.2