fix: Read file-like KVS values before upload and reject unencodable ones #970

Job	Run time
PR title check	8s
Checks / Lint check / Lint check (3.12)	9s
Checks / Doc check / Docs check	1m 16s
Checks / Type check / Type check (3.13)	14s
Checks / Type check / Type check (3.11)	9s
Checks / Docstrings check	10s
Checks / Website lint check	34s
Checks / Actions lint check	32s
Checks / Type check / Type check (3.14)	14s
Checks / Lint check / Lint check (3.14)	10s
Checks / Type check / Type check (3.12)	10s
Checks / Spell check	6s
Checks / Package check	16s
Checks / Integration tests (3.14, ubuntu-latest)	2m 57s
Checks / Markdown lint check	44s
Checks / Lint check / Lint check (3.13)	10s
Checks / Unit tests / Unit tests (windows-latest, 3.12)	1m 4s
Checks / Unit tests / Unit tests (ubuntu-latest, 3.12)	49s
Checks / Unit tests / Unit tests (ubuntu-latest, 3.14)	49s
Checks / Image lint check	7s
Checks / Integration tests (3.11, ubuntu-latest)	2m 52s
Checks / Lint check / Lint check (3.11)	8s
Checks / Unit tests / Unit tests (ubuntu-latest, 3.13)	51s
Checks / Unit tests / Unit tests (windows-latest, 3.14)	54s
Checks / Unit tests / Unit tests (windows-latest, 3.13)	1m 10s
Checks / Unit tests / Unit tests (windows-latest, 3.11)	1m 14s
Checks / Unit tests / Unit tests (ubuntu-latest, 3.11)	52s
	18m 49s

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