feat(format_args): make them default constructible and add empty() fu… #488

Job	Run time
memcheck	7m 2s
sanitize	6m 52s
checks	1m 3s
coverage	1m 28s
size-test	28s
size-test-embedded (ci-size-coverage-embedded)	47s
unit-tests (ubuntu-22.04, gcc-11, Debug)	3m 28s
size-test-embedded (ci-size-coverage-embedded-nano)	47s
unit-tests (ubuntu-22.04, gcc-11, Release)	2m 18s
unit-tests (ubuntu-22.04, gcc-12, Debug)	3m 39s
unit-tests (ubuntu-22.04, gcc-12, Release)	2m 30s
unit-tests (ubuntu-24.04, gcc-13, Debug)	3m 44s
unit-tests (ubuntu-24.04, gcc-13, Release)	2m 40s
unit-tests (ubuntu-24.04, gcc-14, Debug)	3m 44s
unit-tests (ubuntu-24.04, gcc-14, Release)	2m 49s
unit-tests (ubuntu-22.04, clang-16, Debug)	3m 55s
unit-tests (ubuntu-22.04, clang-16, Release)	2m 43s
unit-tests (ubuntu-22.04, clang-17, Debug)	3m 33s
unit-tests (ubuntu-22.04, clang-17, Release)	2m 42s
unit-tests (ubuntu-24.04, clang-18, Debug)	4m 11s
unit-tests (ubuntu-24.04, clang-18, Release)	3m 5s
	1h 3m 28s

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