Use sinc in ChudleyElliottJumpDiffusion width dependency expression once supported for Parameters #272

ChudleyElliottJumpDiffusion._write_width_dependency_expression currently writes
the Chudley-Elliott width as

(hbar / tau) * (1 - sin(Q * l.value) / (Q * l.value))

because sinc isn't available for Parameters yet. This also affects a few cases in the unit tests. Support for it is being
implemented in easyscience/core:

• Add maths module for Parameters & DescriptorNumbers with variance and bounds propagation core#329

Once that PR is merged and released, and dynamics-lib depends on a version that
includes it, replace the explicit sin(x)/x with sinc.

To do:

• Wait for Add maths module for Parameters & DescriptorNumbers with variance and bounds propagation core#329 to be merged and released.
• Bump the easyscience dependency to a version that includes it.
• Update _write_width_dependency_expression (and the matching dependency map
  expression) to use sinc.
• Check that calculate_width and the dependency-based widths still agree in the tests.
• Update and test test_calculate_width_sinc_stability
• Remove the TODO comment that points to this issue.

Raised in review of #246.