Remove usage of internal header encoding API #3753

Job	Run time
changes	3s
check-lockfile	4s
lint-crlf	4s
lint-newsfile	41s
Typechecking	1m 26s
check-sampleconfig	44s
check-schema-delta	40s
lint	27s
lint-clippy	0s
lint-pydantic	1m 14s
lint-clippy-nightly	0s
lint-readme	0s
lint-rustfmt	0s
linting-done	2s
calculate-test-jobs	9s
trial-olddeps	8m 48s
complement (monolith, SQLite)	13m 31s
portdb (3.8, 11)	3m 12s
complement (monolith, Postgres)	14m 45s
portdb (3.11, 15)	3m 18s
cargo-bench	0s
complement (workers, Postgres)	21m 3s
cargo-test	0s
trial-pypy	0s
trial (3.8, sqlite, all)	6m 44s
sytest (focal)	8m 56s
trial (3.8, postgres, 11, all)	14m 38s
sytest (focal, postgres)	10m 21s
trial (3.8, sqlite)	5m 23s
sytest (focal, multi-postgres, workers)	22m 7s
sytest (focal, multi-postgres, workers, asyncio)	19m 23s
export-data	2m 11s
tests-done	3s
	2h 39m 57s

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