Fix conversion from symbolic series to lazy Laurent series

[yashashwi-s]

Fix conversion from symbolic series to lazy Laurent series

This PR partially fixes issue #39840, addressing only the first error when converting symbolic series to lazy Laurent series.

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Original Issue

When attempting to convert a symbolic series:

var("x")
f = (1/x + sqrt(x + 1)).series(x)

The following error occurred with LazyLaurentSeriesRing:

ValueError: the valuation must be specified

The second error with LazyPowerSeriesRing remains unresolved:

TypeError: Substitution using function-call syntax and unnamed arguments has been removed...

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🔧 Fix Implementation

Explicit handling for SymbolicSeries objects was added to the _element_constructor_ method to properly determine the valuation and extract coefficients.

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✅ Testing

Manual testing confirms that the LazyLaurentSeriesRing conversion now works correctly:

var("x")
f = (1/x + sqrt(x + 1)).series(x)
LazyLaurentSeriesRing(QQ, "x")(f)  # Works now

⚠️ The LazyPowerSeriesRing conversion issue will be addressed in a separate PR.

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📋 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

[user202729]

Do add some doctest.