Improve AsepriteBinaryReader and DeflateStream usage

[SaxxonPike]

Prerequisites

• I have verified that there are no existing pull requests that would overlap with this pull request.
• I have verified that I am following the guidelines as outlined in this project's contribution policy
• I Have verified that this pull request adheres to this project's code of conduct.
• I have written a descriptive title for this pull request.
• I have provided appropriate test coverage were applicable.

Description

Improvements to AsepriteBinaryReader

• Instead of a heap-allocated small buffer with .AsSpan(), use stackalloc
  • In this case where the buffer is very small, stackalloc is very fast
• Reconcile Aseprite's distinction between fixed and float:
  • Fixed point values are stored as 16:16 (that is, 16-bit integer and 16-bit fraction)
  • Floating point values are stored as single-precision IEEE values

DeflateStream to ZlibStream:

• Instances of DeflateStream now use ZlibStream
  • We can defer the responsibility of handling the header to the .NET standard library

Non-functional changes:

• Documentation grammar

Related Issue Ticket Numbers

• n/a