Expose coefficients of extension fields #533

Job	Run time
Clippy lint checks	1m 16s
Wasm-compatibility (wasm32-unknown-unknown)	2m 32s
Bench (default)	4m 52s
Rustfmt	37s
Wasm-compatibility (wasm32-wasi)	2m 29s
Bench (asm)	6m 43s
Test (default)	6m 54s
Bench (bn256-table)	6m 51s
Spell Check with Typos	7s
Test (bn256-table)	7m 2s
Test (derive_serde)	6m 52s
Test (asm)	6m 35s
	52m 50s

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