Fix missing closing tags in multi-page PAGE XML output

[Copilot]

Multi-page TIFF files produce malformed PAGE XML with missing </Page> closing tags for all pages except the last, causing validation failures.

Changes

• GetPAGEText(): Add </Page> closing tag at end of method (line 1126)
• EndDocumentHandler(): Remove </Page> tag, retain only </PcGts> (line 686)
• Test Added: Added PAGEXMLMultiPageClosingTags test in unittest/baseapi_test.cc to validate proper tag closure for multi-page documents

Each page now generates a complete <Page>...</Page> element. The document handler manages only the outer envelope, matching the pattern used in altorenderer.cpp.

Before:

<PcGts>
  <Page>...      <!-- unclosed -->
  <Page>...      <!-- unclosed -->
  <Page>...</Page>
</PcGts>

After:

<PcGts>
  <Page>...</Page>
  <Page>...</Page>
  <Page>...</Page>
</PcGts>

Testing

The new test validates:

• Each page has exactly one opening <Page> tag
• Each page has exactly one closing </Page> tag
• Opening and closing tags match (balanced XML)
• Individual page outputs don't contain document envelope tags
• Multiple pages each close properly

Original prompt

Please create a pull request which fixes this bug.

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[stweil]

@copilot, please rebase this PR to the latest code in the main branch. In addition, it would be nice to add a CI test for this issue.

[Copilot]

@copilot, please rebase this PR to the latest code in the main branch. In addition, it would be nice to add a CI test for this issue.

Done! The PR is now rebased on the latest main branch (the typo fix was already merged in 9c393bb). I've also added a CI test PAGEXMLMultiPageClosingTags in unittest/baseapi_test.cc that validates:

• Each page has exactly one opening and closing <Page> tag
• Individual page outputs don't contain document envelope tags
• Multiple pages each close properly

Commit: b8e2455