[FIX]: Add ATSC VCT virtual channel numbers and call signs to XMLTV output

[x15sr71]

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Description

XMLTV channel definitions now include ATSC VCT-derived virtual channel numbers (major.minor) and call signs, emitted as separate <display-name> elements and associated with the existing channel ID (program number).

Example output:

<channel id="1">
  <display-name>5.1</display-name>
  <display-name>KPIX-TV</display-name>
</channel>

This follows the XMLTV DTD (display-name+) and the approach discussed in #1835

Note: This PR also adds a changelog entry for the previously merged PR #1773

[cfsmp3]

Excellent work! This is a clean, well-implemented enhancement from a proven contributor.

Review Results

• ✅ All Linux builds pass
• ✅ Correct ATSC A/65 bit extraction for major/minor channel numbers
• ✅ Proper UTF-16BE to UTF-8 conversion for VCT short_name
• ✅ Good edge case handling (empty names, whitespace trimming, fallbacks)
• ✅ XML-safe output using EPG_fprintxml()
• ✅ XMLTV DTD compliant (multiple display-name elements)
• ✅ Rust FFI properly updated
• ✅ Changelog updated (including missing entry for #1773)

ATSC A/65 Verification

The bit extraction is correct per Section 6.4:

major_channel_num = ((offset[14] & 0x0F) << 6) | ((offset[15] & 0xFC) >> 2);  // ✅
minor_channel_num = ((offset[15] & 0x03) << 8) | offset[16];                   // ✅

Great follow-up to #1773 - the ATSC XMLTV support is now much more complete!

Approved and merging.