Fix the meter for remote calls inside a transaction

An order service holds one database transaction open while it charges the card and sends the email, and under load the connection pool runs dry. The team wants a meter that replays a request's steps and adds up the time spent on remote calls while a transaction is open.

An assistant wrote external_ms_in_transaction(steps). It is in the editor. It has a bug. Find it and fix it.

Input and output:

• steps: the request's steps, in order. Each one is "begin", "commit", "rollback", or "kind|name|duration_ms", such as "http|charge|800".
• Return the total milliseconds, as an integer.

Rules the tests check:

• Keep a depth that starts at 0. "begin" adds 1. "commit" and "rollback" each take 1 away, but never below 0. A nested "begin" joins the outer transaction, so the connection stays held until the depth is back to 0.
• A transaction is open while the depth is above 0. A transaction still open at the end of the list counts the same.
• Any other step must split on | into exactly 3 parts: kind, name and duration. Skip it otherwise.
• The duration must be 1 to 15 digits (0 to 9) and nothing else. Leading zeros are fine. Skip the step otherwise.
• The kind "db" is local database work and never counts. Every other kind is a remote call: "http", "queue", "grpc", an empty kind, anything.
• Add a remote call's duration when a transaction is open. The name part does not matter and can be empty.
• Matching is case sensitive. "DB" is a remote kind, and "Begin" is not "begin", so it is skipped like any step without 3 parts.
• No steps returns 0.