fix(operations.files): shell-quote files.block content

[wowi42]

Summary

files.block passed the block content to awk as a positional argument wrapped in raw quote characters via string concatenation instead of proper shell quoting. Any content containing double quotes, single quotes, $(...) or backticks broke the generated command.

Reproduction (from upstream issue):

files.block(path="/root/.bashrc", content='eval "$(zoxide init --cmd cd bash)"')

The create path used a heredoc, so the first run succeeded; the second run (update existing block) failed with sh: Syntax error: "(" unexpected. The line-match path was affected the same way. Unquoted content was also a shell-injection vector.

Fix

• Update and line-match paths now pass content through QuoteString (shlex.quote).
• The create-path heredoc delimiter is quoted (<<'PYINFRAHERE') so the body is literal too.
• Content is always written verbatim and is never expanded on the remote host. This also removes the previous limitation where content containing raw single quotes could break.
• try_prevent_shell_expansion no longer affects quoting (content is always literal); it is kept and accepted for backwards compatibility and documented as deprecated.

Tests

• 3 new YAML fixtures reproducing the issue across the update, line-match and no-file code paths with ", ' and $(...) in the content (written test-first, confirmed failing before the fix).
• 7 pre-existing fixtures that encoded the old unsafe quoting updated to the corrected, shell-safe output.
• Full suite passes (1737 passed); scripts/dev-lint.sh clean (ruff, format, mypy, arguments-sync).

Fixes the bug reported upstream: pyinfra-dev#1758

[wowi42]

Superseded by upstream PR pyinfra-dev#1759.