refactor: validate `Fdt` on construction #282

Job	Run time
Cargo check	13s
Build with each feature combination	8s
Code formatting checks	17s
Minimal dependency versions build	20s
Clippy lint checks	18s
Machete dependencies checks	1m 11s
Build & test (stable, windows-latest)	42s
Build & test (stable, macos-latest)	18s
Build & test (1.88, macos-latest)	28s
Build & test (nightly, macos-latest)	23s
Build & test (1.88, ubuntu-latest)	19s
Build & test (nightly, windows-latest)	42s
Build & test (1.88, windows-latest)	49s
Build & test (stable, ubuntu-latest)	17s
Build & test (nightly, ubuntu-latest)	16s
Miri test	1m 18s
	7m 59s

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