Initialize all unused GPIO with pull-ups to prevent power draw

**Describe the problem you have**
Floating GPIO causes unnecessary power draw and instability

**Please describe your use case for this integration and alternatives you've tried:**
Alternative: manually setting all unused GPIO to input with pull-up

**Additional context**
https://github.com/esphome/issues/issues/1950
https://github.com/esphome/issues/issues/5085
https://github.com/esphome/feature-requests/issues/2586
https://www.reddit.com/r/Esphome/comments/ppzd08/is_it_normal_for_a_smart_plug_to_feel_warmer_when/
https://community.home-assistant.io/t/esp-overheat-without-ha/508317/3
https://community.home-assistant.io/t/device-overheating-on-esphome-but-fine-on-tasmota/464181/8

**Suggested feature**
ESPHome should enumerate all unused GPIOs (I think it should have that information in board config?) and set default for all as GPIO input with pull-up. Example from https://github.com/esphome/issues/issues/5085#issuecomment-1897557212:
```
binary_sensor:
- platform: gpio
id: gpio16
pin:
number: GPIO16
mode:
input: true
pullup: true
```

Start by reviewing the board configuration information referenced in the request and the existing GPIO initialization entry points. The issue does not name files or tests; done would require a defined way to identify unused pins and verify that they receive input pull-ups without affecting configured pins.

Written by the indexing model from the issue text.