refactor: validate `Fdt` on construction #280

Job	Run time
Cargo check	12s
Minimal dependency versions build	20s
Build with each feature combination	18s
Clippy lint checks	12s
Machete dependencies checks	1m 7s
Code formatting checks	14s
Build & test (stable, windows-latest)	45s
Build & test (nightly, windows-latest)	41s
Build & test (nightly, ubuntu-latest)	16s
Build & test (1.88, ubuntu-latest)	18s
Build & test (nightly, macos-latest)	24s
Build & test (stable, macos-latest)	24s
Build & test (stable, ubuntu-latest)	10s
Build & test (1.88, macos-latest)	24s
Build & test (1.88, windows-latest)	54s
Miri test	1m 9s
	7m 48s

Provide feedback