Add .npmignore

[aaroncameron-wk]

Reason for change

npm pack intends to exclude files included in .gitignore, so the dist/ directory should have been excluded from packages published in the past. A recent npm release included a correction to a faulty handling of .gitignore, so dist/ now became excluded (as intended by npm pack) in releases starting with 1.4.23.

Description of change

To resolve the issue, we can decouple our .gitignore entries from what's included in the npm package by adding a .npmignore file that npm pack considers as an override to .gitignore for its purposes.

Steps to Test

For both an older version of node (20.11.1, used to release 1.4.22), and the lastest version of node, I ran npm pack and compared the file listing output to confirm no unexpected differences.

One could repeat this to confirm, or simply just confirm afterwards that the released package looks as expected.

review: @Arelle/arelle @paulwarren-wk

[aviary2-wf]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure

• Verify aviary.yaml coverage of security relevant code

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