[FEATURE] Copy some metadata to subparsers

[eseiler]

Subparsers do not have any metadata set.
When you already set metadata for the top-level parser, you need to do so again for the subparser.

This PR makes it so that some metadata is copied to the subparser:

Metadata	Copied?
app_name	⛔
version	✅
short_description	❌
author	✅
email	✅
date	✅
url	✅
short_copyright	✅
long_copyright	✅
citation	✅
man_page_title	❌
man_page_section	❌
description	❌
synopsis	❌
examples	❌

Notes

• copy_metadata_to_subparser could also be a member function of parser_meta_data for better encapsulation.
• app_name is overwritten.
• I don't think it makes sense to copy the other metadata too?

Example

Excerpts of the help page for top-level and subcommand.

Before

# Top-level
VERSION
    Last update: 2025-08-15
    FPGAlign version: 1.0.0
    Sharg version: 1.1.2-rc.1
    SeqAn version: 3.4.0-rc.4

LEGAL
    Author: Enrico Seiler
    SeqAn Copyright: 2006-2024 Knut Reinert, FU-Berlin; released under the 3-clause BSDL.

# Subcommand
VERSION
    Last update: 
    FPGAlign-build version: 
    Sharg version: 1.1.2-rc.1
    SeqAn version: 3.4.0-rc.4

After

# Top-level
VERSION
    Last update: 2025-08-15
    FPGAlign version: 1.0.0
    Sharg version: 1.1.2-rc.1
    SeqAn version: 3.4.0-rc.4

LEGAL
    Author: Enrico Seiler
    SeqAn Copyright: 2006-2024 Knut Reinert, FU-Berlin; released under the 3-clause BSDL.

# Subcommand
VERSION
    Last update: 2025-08-15
    FPGAlign-build version: 1.0.0
    Sharg version: 1.1.2-rc.1
    SeqAn version: 3.4.0-rc.4

LEGAL
    Author: Enrico Seiler
    SeqAn Copyright: 2006-2024 Knut Reinert, FU-Berlin; released under the 3-clause BSDL.

[seqan-actions]

Documentation preview available at https://docs.seqan.de/preview/seqan/sharg-parser/285

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.46%. Comparing base (4480a90) to head (a6f81c3).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #285      +/-   ##
==========================================
+ Coverage   94.37%   94.46%   +0.08%     
==========================================
  Files          20       20              
  Lines        1637     1663      +26     
  Branches       47       47              
==========================================
+ Hits         1545     1571      +26     
  Misses         92       92              

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