Speed up net filtering by names in the simplifier

[ordinarymath]

Currently the check to filter out a net by name in the simplifier is complicated and slow https://github.com/HOL-Theorem-Prover/HOL/blob/24e40cd1c7f7e235a5c9f32f692c0d9ae04ddb2b/src/simp/src/simpLib.sml#L272C1-L275C66

            val checknamepart =
                patbase = ssnm orelse
                "rewrite:" ^ patbase = ssnm orelse
                String.isPrefix ("rewrite:" ^ patbase ^ ".") ssnm

This should only be one check and more information currently stored in the string should move to conv_info https://github.com/HOL-Theorem-Prover/HOL/blob/24e40cd1c7f7e235a5c9f32f692c0d9ae04ddb2b/src/simp/src/simpLib.sml#L233C1-L234C76

[mn200]

It's slow but called very infrequently; this doesn't feel like a high priority.