tao_param_value_routine: handle long expressions

[jsberg-bnl]

You have this annoying user that insists on using long complex expressions. tao_param_value_routine was truncating sub-expressions because its intermediate strings weren't long enough. This patch fixes the problem. FYI error output from the buggy version looked like:

[ERROR | 2024-AUG-16 17:26:43] tao_evaluate_expression:
    UNMATCHED "("
    IN EXPRESSION: max(abs(ele::md[b_field]+ele::md[b1_gradient]*data::md.x
[ERROR | 2024-AUG-16 17:26:43] tao_evaluate_expression:
    ERROR IN EVALUATING EXPRESSION: max([max(abs(ele::mf##1[b_field]+ele::mf##1[b1_gradient]*data::mf.xm|model)),max(abs(ele::mf##1[b_field]+ele::mf##1[b1_gradient]*data::mf.xp|model)),max(abs(ele::md[b_field]+ele::md[b1_gradient]*data::md.xm|model)),max(abs(ele::md[b_field]+ele::md[b1_gradient]*data::md.xm|model))])
    CANNOT EVALUATE: [max(abs(ele::mf##1[b_field]+ele::mf##1[b1_gradient]*data::mf.xm|model)),max(abs(ele::mf##1[b_field]+ele::mf##1[b1_gradient]*data::mf.xp|model)),max(abs(ele::md[b_field]+ele::md[b1_gradient]*data::md.xm|model)),max(abs(ele::md[b_field]+ele::md[b1_gradient]*data::md.xm|model))]
[ERROR | 2024-AUG-16 17:26:43] tao_set_invalid:
    CANNOT EVALUATE EXPRESSION: max([max(abs(ele::mf##1[b_field]+ele::mf##1[b1_gradient]*data::mf.xm|model)),max(abs(ele::mf##1[b_field]+ele::mf##1[b1_gradient]*data::mf.xp|model)),max(abs(ele::md[b_field]+ele::md[b1_gradient]*data::md.xm|model)),max(abs(ele::md[b_field]+ele::md[b1_gradient]*data::md.xm|model))])
    FOR DATUM: field[1] with data_type: expression:max([max(abs(ele::mf##1[b_field]+ele::mf##1[b1_gradient]*data::mf.xm|model)),max(abs(ele::mf##1[b_field]+ele::mf##1[b1_gradient]*data::mf.xp|model)),max(abs(ele::md[b_field]+ele::md[b1_gradient]*data::md.xm|model)),max(abs(ele::md[b_field]+ele::md[b1_gradient]*data::md.xm|model))])