fix: child execs should inherit parent argument values

[jahvon]

Refactors how arguments are handled in the serial and parallel runners to ensure that they are passed down to deeply nested exec steps. It does require that expected args / envkeys are defined on the parent or that the parent doesnt define args all together.

Includes some related code renames / cleanup in other packages.

[codecov]

Codecov Report

❌ Patch coverage is 65.02463% with 71 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/runner/parallel/parallel.go	60.37%	14 Missing and 7 partials ⚠️
internal/runner/serial/serial.go	63.63%	14 Missing and 6 partials ⚠️
internal/utils/env/env.go	50.00%	10 Missing and 2 partials ⚠️
types/executable/arguments.go	0.00%	7 Missing ⚠️
internal/runner/launch/launch.go	0.00%	3 Missing ⚠️
internal/runner/render/render.go	0.00%	3 Missing ⚠️
internal/templates/templates.go	50.00%	1 Missing and 1 partial ⚠️
internal/utils/env/args.go	95.23%	1 Missing and 1 partial ⚠️
cmd/internal/exec.go	83.33%	0 Missing and 1 partial ⚠️

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