follow-up to #3343: review uses of bufio.Scanner

### What is the problem you're trying to solve

As discussed in https://github.com/containerd/nerdctl/issues/3343, the usage of bufio.Scanner when we do not have the control over the length of the message processed by the scanner can put the Scanner in a I/O error state failing silently and blocking the process sending a message.

@apostasie recommend that the usage of bufio.Scanner across the project is revisited.

### Describe the solution you'd like

A solution is suggested with https://github.com/containerd/nerdctl/pull/3366 but might not be a "one size fit all solution".

### Additional context

[Documentation](https://pkg.go.dev/bufio#Scanner)

The documentation state the following:

Scanning stops unrecoverably at EOF, the first I/O error, or a token too large to fit in the [Scanner.Buffer](https://pkg.go.dev/bufio#Scanner.Buffer). When a scan stops, the reader may have advanced arbitrarily far past the last token. Programs that need more control over error handling or large tokens, or must run sequential scans on a reader, should use [bufio.Reader](https://pkg.go.dev/bufio#Reader) instead.