Support atol/rtol in rum.toml simulation configs

[jgoppert]

rumoca sim supports separate --atol and --rtol CLI flags, but the rum.toml / rum.<profile>.toml scenario schema does not yet expose matching [sim] fields.

Current gap:

• [sim] accepts dt, t_end, solver, output, test, and mode only.
• The scenario parser denies unknown fields, so adding atol = ... or rtol = ... currently fails instead of configuring solver tolerances.
• The interactive runner still uses fixed tolerance defaults instead of scenario-provided values.

Desired shape:

• Add optional [sim].atol and [sim].rtol fields.
• Validate both as finite positive values.
• Apply clear precedence: CLI > TOML > Modelica experiment(Tolerance=...) > backend defaults.
• Wire both batch rumoca sim -c ... and interactive runner paths.
• Update rumoca sim init, docs, and scenario config tests.

[jgoppert]

Now supported.