fix(vars): carry custom Field attrs by reference, not deepcopy #1615

Job	Run time
discover	8s
build (reflex-components-code, packages/reflex-components-code/)	23s
build (reflex, .)	37s
build (integrations-docs, packages/integrations-docs/)	20s
build (reflex-docgen, packages/reflex-docgen/)	16s
build (reflex-components-gridjs, packages/reflex-components-gridjs/)	23s
build (reflex-components-sonner, packages/reflex-components-sonner/)	16s
build (reflex-components-internal, packages/reflex-components-internal/)	35s
build (reflex-components-plotly, packages/reflex-components-plotly/)	23s
build (hatch-reflex-pyi, packages/hatch-reflex-pyi/)	15s
build (reflex-components-core, packages/reflex-components-core/)	21s
build (reflex-components-markdown, packages/reflex-components-markdown/)	25s
build (reflex-components-lucide, packages/reflex-components-lucide/)	17s
build (reflex-components-moment, packages/reflex-components-moment/)	17s
build (reflex-components-react-player, packages/reflex-components-react-player/)	20s
build (reflex-components-dataeditor, packages/reflex-components-dataeditor/)	25s
build (reflex-components-recharts, packages/reflex-components-recharts/)	16s
build (reflex-hosting-cli, packages/reflex-hosting-cli/)	18s
build (reflex-site-shared, packages/reflex-site-shared/)	38s
build (reflex-base, packages/reflex-base/)	15s
build (reflex-components-radix, packages/reflex-components-radix/)	24s
	7m 32s

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