Silence various type conversion warnings

[sagamusix]

Hello Geraint! First off, thank you for this fantastic high-quality library. I intend to use this in OpenMPT for offline sample processing, replacing two older libraries we currently use for pitch-shifting and time-stretching.

This PR intends to silence a couple of warnings I got when compiling with MSVC with high warnings levels; similar warnings may be observed with other compilers if the warning levels are set sufficiently high. Here's a few notes on what I did:

• Most of the warnings revolve around double -> float conversions when instantiating the Stretch template with a float data type rather than double.
• std::min<int>(someInt, someFloat) generates warnings in MSVC, so these constructs have been changed to std::min(someInt, static_cast<int>(someFloat)).
• There was also a variable shadowing warning that I silenced.

[sagamusix]

Rebased on current main, with only the changes that directly affect this repository. I can later provide the remaining fixes against the signalsmith-linear repository. @geraintluff could you please take a look? :)

[geraintluff]

Awesome - thanks for updating. I'll look at it this coming week!