Report runtime conditions of every ::object-id a block selects

[biodranik]

Follow-up to #41.

What

updateStyles() applies a declaration block to each ::object-id its selector group
matches, but get_runtime_conditions() still used testChains() and reported only the
first matching chain's conditions. libkomwm builds one drule variant per reported
condition set, so for a group that mixes object-ids and per-chain runtime conditions the
second object-id's variant was never enumerated, and applyStylesTo()'s
filter_by_runtime_conditions check silently dropped its styles:

node|z4-[place=city][population>=1000],
node|z4-[place=city][population>=500]::int_name,
{text: name;}

reported conditions -> ['population>=1000']
resulting styles    -> ['::default']          # ::int_name lost

Collect the conditions of all matched object-ids instead, so the two functions agree on
what a block selects.

testChains() has no callers left afterwards, so it is dropped; its tests point at
testChainsAll(), or straight at Rule.test() where the chooser has a single chain.

Impact

Latent so far — no style in the main repo mixes object-ids with per-chain runtime
conditions inside one block, so the generated drules do not change.

Testing

• python3 -m unittest discover -s tests — 57 tests pass; the new test_runtime_conditions
  fails against master.
• ruff check --target-version=py39 — clean.
• integration-tests/full_drules_gen.py against the main repo's data/ (default, outdoors,
  vehicle; light and dark): the .bin/.txt files and the side files (types.txt,
  classificator.txt, visibility.txt, colors.txt, patterns.txt, priorities) are
  byte-identical to master's output. Generation time unchanged (~11.1 s either way).