Fixes # .

Summary/Motivation:

@dallan-keylogic found a particularly nefarious bug where turning on the handling of scaling in the NLv2 writer would fail to scale the linear coefficients of named expressions (Expression components) used in nonlinear contexts. This PR resolves the bug and adds a test for scaling named Expression objects in nonlinear contexts (slightly modified from @dallan-keylogic's MWE).

Changes proposed in this PR:

• update _write_v_line to scale the linear term coefficients.
• add a test covering this error

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