[Project Suggestion] Lower the overclock setting of the Pico 2 config slightly.

[Geekachuqt]

The Pico 2 overclock settings are currently set to 300MHz. Depending on silicon lottery, this may cause instability. I have personally had a roughly 25% success rate with getting pico 2s to run at 300 MHz. I recommend lowering the overclock to 275MHz. All of my Picos (tested 7) have ran at this speed with no issues.

[roryjamesallen]

Adding to this, user 'Visions' in Discord has had issues with 3rd party (Tenstar) RP2350 boards and has fixed it by removing or reducing the overclocking amount. It probably is safest to reduce even if the errors aren't necessarily found consistently with officially supported boards. The difference between 300 and 275 in user experience isn't likely to be much worse.

[chrisib]

I'm thinking we may actually want to revert a change from several months (maybe even a couple of year?) ago where I changed the explicit CPU frequency to the {overclock|normal|underclock} strings.

The reasoning at the time was that we only supported the Pico 1 officially and the other boards were in a sort of experimental limbo, and exposing the raw CPU frequency was just too complicated for most users to want to care about. But now that we've got more boards supported that seem to need finer-tuning over the CPU frequency I think it's reasonable to reconsider that change.

To avoid compatibility issues we could keep the existing strings as defaults and add a new CPU_FREQ_HZ configuration field that can be used as an override? It defaults to None, but if it's specified then we can apply the user-specified clock frequency. That would allow some fine-tuning outside of our normal channels. This way we can keep the default higher overclock speed for the official Pico2 boards (which seem to be working well at that rate -- mine is at least), but also allowing users with third-party boards the flexibility to adjust as needed.