Update nuspec to place library files under nano TFM

[Copilot]

NuGet packages were placing library files directly under lib\ instead of the correct lib\netnano1.0\ target framework folder, and dependencies lacked a .NETnanoFramework1.0 group declaration.

Changes to nanoFramework.System.Device.Spi.nuspec

• Dependencies: Wrapped all dependencies in a <group targetFramework=".NETnanoFramework1.0"> element
• Files: Replaced five individual file entries (dll, pdb, pdbx, pe, xml) with a single wildcard targeting lib\netnano1.0

<dependencies>
  <group targetFramework=".NETnanoFramework1.0">
    <dependency id="nanoFramework.CoreLibrary" version="2.0.0-preview.35" />
    <dependency id="nanoFramework.Runtime.Events" version="2.0.0-preview.8" />
    <dependency id="nanoFramework.System.Device.Gpio" version="2.0.0-preview.9" />
  </group>
</dependencies>
...
<file src="System.Device.Spi\bin\Release\System.Device.Spi.*" target="lib\netnano1.0" />

Follows the pattern established in nanoframework/System.Device.Adc@aab7bca.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update nuspec to place library under nano TFM</issue_title>
<issue_description>### Details about task
Most of the nuspec files are not using the correct location to place the files.
Files (DLL, PE, PDBX and XML for IntelliSense) should be placed under "lib\netnano1.0" (currently are being placed under "lib" only.
Also they should declare a dependency group for ".NETnanoFramework1.0" target framework.
At the same time those still naming the various file types should use a wildcard instead (e.g. "...\Release\mscorlib.*).
The correct pattern should be (take this nuspec as sample):
nanoframework/System.Device.Adc@aab7bca

Do not change anything else on the nuspec file.

Description

</issue_description>

Comments on the Issue (you are @copilot in this section)

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