node.chipid() returns "0x_unknown" for ESP32xx chips

[serg3295]

• This PR is for the dev branch rather than for the release branch.
• This PR is compliant with the other contributing guidelines as well (if not, please describe why).
• I have thoroughly tested my contribution.
• The code changes are reflected in the documentation at docs/*.

The reason for this change is that the nodemcu-tool utility expects the node.chipid() command to exist in the Lua environment.
However, ESP32c6|s2|h2 chips do not have a chipid, so node.chipid() function will return 0x_unknown for these chips.

[marcelstoer]

ESP32c6|s2|h2 chips do not have a chipid, so node.chipid() function will return 0x_unknown

Shouldn't the docs in node.md mention this? There's a - now outdated - comment in #3652.