resolve #2563

amend b8921b9a89

* customize our multipliers. accuracy is a generic multiplier, mostly
  depends on the environment temperature (see datasheet). sensitivity is
  a ratio between the currently set mtreg value and the default
  e.g. for mtreg 31, sensitivity is .45; for mtreg 69, sensitivity is 1.
* non-blocking pre(); since we have tick(), just wait until the reading
  is available instead of stopping everything else in the sensor loop
* more specific error state when we are not ready to return a value

return half of raw value in both modes involving it
resolve #2550 (just for the sensor, no global setting yet)

ref. #2483, #2546 and #2554
instead of waiting for our time window, attempt to read & parse everything
discard unknown data more frequently, and attempt to store more data as well

resolve #2558
resolve #2559

- revert to ignoring rgb in color+white+cct case by resetting all its
  inputs to minimum and only controlling white channels
- ignore ww and cw in rgb+cct case; use approximated color, thus allowing
  us to set a different 'cold temperature' limit
- fix webui layout rules based on root element class(es) and consistent
  order for our control elements that does not depend on the order in which
  `processData` handles configuration kvs
- internal refactoring to flatten input processing funcs selection
  (to possibly replace our boolean flags with a simple list)

...and since it still causes hwdt crashes

ref. #2547, tell gpio side that we don't need any init

may do weird stuff after runtime pin changes, since we won't know our
new pins due to the order of setup() functions

same as original fix for the Core
fix footer into a single line and add UTC alias notice

make use of our apply() objects for value replacement in-place
also revert the white channel mode change that ignores rgb output factor

amends 94f0786ed5

looking at <...> TZ values, previous version seemed true

refer to our docs for the script output
see #2548

register channels with their respective tags, instead of using count
both on backend and frontend

revert to useCCT mireds slider rule, disallow white channels with useWhite

resolve #2554

make use of cse7766 calculation for factor, too
thanks to @Kaan88

remove reactive power ratio from base sensor as well, since it does not
seem to be used anywhere else (...and does not really make sense in most
situations when sensor inputs are using common gain)

avoid optimizing out function call when `&&` comparison is always false
resolve #2555

* clean-up useless stream read() / flush(), rely on timer and internal state
  avoids wdt reset with sensors looping on available()
* fix some instances of `available()` in boolean context to use `>0`
  (not everything returns sign, but if it does - we are in trouble)
* util func to read available bytes from the stream using buffered
  interface instead of 1 byte at a time

color temperature applies to input values as and / or
- rgb channels scale, when cct mode is enabled w/ color
- white channel(s), moving between warm and cold

remove two rgb scalers applied one after the other in favour of two
distinct variants - we either subtract common value from rgb or use
mireds as a scale for both rgb and ww+cw
restore brightness control as well

fix invalid prometheus syntax `strconv.ParseFloat: parsing "/0": invalid syntax`
fix another instance of remove('/')

rgb only applies to the first 3, group applies to all

avoid going out-of-bounds in phases loop
small adjustments to the variable loading

notice about buffering and its impact
and avoid using strcmp, just compare bytes

* error code is not buffered through our handler object.
  while espasync code does strlen, what it returns is mostly random.
  (old request parts, weird data, etc.)
* reworked buffer class to avoid an extra allocation on top of the
  existing vector data buffer. plus, simple function pointer as well

* correct id=... and element references, partial changes to element
  order were not using the new global 'light' container
* separate block for picker, does not seem consistent to depend on json
  key order when processing device cfg
* visibility != display; make sure color picker is hidden when there is
  no color control, but not visible when color is on but state is off