Run examples in float32 precision

[pnkraemer]

Not in float64 precision. This will also expose some potential issues in numerically stable implementations.

[pnkraemer]

At least the non-advanced examples that do not solve complicated problems.

[pnkraemer]

For future reference:

• Investigate all uses of jnp.sqrt(jnp.dot(...))
• Investigate all uses of ** operations, e.g. l_obs**2
• Change _adaptive.AdaptiveIVPSolver.numerical_zero to a value that depends on floating-point precision
• Resolve Minstep and maxstep in step-size adaptation #168 (which improves the debuggability of the "close-to-numerical-failure" cases)
• Introduce a "success=True/False" flag in IVP solution (which improves the debuggability of the "close-to-numerical-failure" cases)