Add module-level docs for Curve #51048

Job	Run time
toml	1m 56s
miri	9m 59s
build (windows-latest)	5m 54s
check-bevy-internal-imports	5s
build (ubuntu-latest)	2m 44s
check-doc	7m 23s
build (macos-latest)	2m 12s
ci	2m 48s
check-missing-examples-in-docs	30s
typos	9s
check-missing-features-in-docs	29s
markdownlint	1m 9s
check-compiles-no-std	19s
check-compiles	4m 37s
build-wasm-atomics	1m 41s
build-wasm	51s
msrv	56s
	43m 42s

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