refactor(BeautifulSoup4): modernize SlackBuild script with better pra…

[visualdendy]

…ctices

• Switch to full English comments and messages
• Use set -euo pipefail for stricter error handling
• Add source tarball existence check
• Improve architecture detection with aarch64 support
• Standardize permissions handling with simpler find commands
• Use consistent quoting and modern bash syntax
• Remove unnecessary PYTHONPATH export (commented out)
• Keep isolated build disabled as per common pure-Python pattern

[github-actions]

reverse dependencies - python/BeautifulSoup4

• desktop/buku
• desktop/variety
• development/jupyter-nbconvert
• development/qbs
• development/redo
• network/holehe
• network/toot
• python/audible
• python/pysass
• python/python3-cloudflare
• python/python3-lxml
• python/python3-pylyrics
• python/subliminal
• system/archmage
• system/linkchecker
• system/routersploit

[github-actions]

⛔️ sbolint - python/BeautifulSoup4 ⛔️

BeautifulSoup4: ERR: BeautifulSoup4.SlackBuild has no newline at EOF
BeautifulSoup4: ERR: BeautifulSoup4.SlackBuild:28: first line of code must be 'cd $(dirname $0) ; CWD=$(pwd)'
BeautifulSoup4: WARN: BeautifulSoup4.SlackBuild:29: lone CWD= assignment is redundant in 15.0 template
sbolint: BeautifulSoup4: errors 2, warnings 1

[visualdendy]

refactor(BeautifulSoup4): modernize SlackBuild script with better practices

• Switch to full English comments and messages
• Use set -euo pipefail for stricter error handling
• Add source tarball existence check
• Improve architecture detection with aarch64 support
• Standardize permissions handling with simpler find commands
• Use consistent quoting and modern bash syntax
• Remove unnecessary PYTHONPATH export (commented out)
• Keep isolated build disabled as per common pure-Python pattern

[willysr]

refactor(BeautifulSoup4): modernize SlackBuild script with better practices

* Switch to full English comments and messages

* Use `set -euo pipefail` for stricter error handling

* Add source tarball existence check

* Improve architecture detection with aarch64 support

* Standardize permissions handling with simpler find commands

* Use consistent quoting and modern bash syntax

* Remove unnecessary PYTHONPATH export (commented out)

* Keep isolated build disabled as per common pure-Python pattern

We do have a rule that source must be placed under same directory so no need to check for existence
We also have template for this, so it should follow the template for readability and maintainability for future usage
https://slackbuilds.org/templates/

plus SBo is designed to work with 15.0, not 15.0+ (current), so this PR can't be accepted