fix(azure): fix double-prosody and 0-1 volume scale when options are provided

[OwenMcGirr]

Problems (fixes #40)

1. Double-nested <prosody>

this.properties defaults (rate="medium", pitch="medium", volume=100) are always truthy, so ensureAzureSSMLStructure always entered the first prosody block and wrapped content with <prosody rate="medium" pitch="medium" volume="100%">. When options were also provided, a second <prosody> element was then wrapped around that, producing invalid double-nested prosody:

<!-- Before fix -->
<voice name="en-US-JennyNeural">
  <prosody rate="fast" pitch="high" volume="80%">
    <prosody rate="medium" pitch="medium" volume="100%">Hello world</prosody>
  </prosody>
</voice>

2. Volume scale mismatch

volume in SpeakOptions is typed 0-100, but callers commonly pass a 0-1 float (e.g. 0.8). The template literal appended % directly, producing volume="0.8%" (essentially silent) instead of volume="80%".

Fix

Merged the two separate prosody-building blocks into one. Options override this.properties defaults. A <prosody> element is only emitted when at least one attribute differs from Azure's implicit defaults (medium/medium/100). Values in the range (0, 1] for volume are detected as fractions and normalised to the 0–100 scale.

<!-- After fix -->
<voice name="en-US-JennyNeural">
  <prosody rate="fast" pitch="high" volume="80%">Hello world</prosody>
</voice>

Tests added

• Single <prosody> element when options are provided
• No <prosody> emitted when all values are at Azure defaults
• volume=0.8 normalises to volume="80%" not "0.8%"