Fix script output dropping last line without trailing newline

[denik]

Changes

Fix experimental.scripts hooks silently dropping the last line of output when it doesn't end with a trailing newline (e.g. printf "done").

Tests

Added acceptance test at acceptance/bundle/scripts/no-trailing-newline/ and unit tests for the script executor.

Running the acceptance test against the previous release demonstrates the bug:

$ go test ./acceptance -run 'TestAccept/bundle/scripts/no-trailing-newline' -useversion 0.296.0

--- Expected
+++ Actual (v0.296.0)
@@ -5,3 +5,2 @@
 line 2
-line without newline
 Name: scripts_no_trailing_newline

v0.296.0 drops "line without newline" because the last line has no trailing \n. The fix correctly includes it.

[github-actions]

Approval status: pending

/acceptance/bundle/ - needs approval

Files: acceptance/bundle/scripts/no-trailing-newline/databricks.yml, acceptance/bundle/scripts/no-trailing-newline/myscript.py, acceptance/bundle/scripts/no-trailing-newline/out.test.toml, acceptance/bundle/scripts/no-trailing-newline/output.txt, acceptance/bundle/scripts/no-trailing-newline/script
Suggested: @andrewnester
Also eligible: @pietern, @lennartkats-db, @shreyas-goenka, @anton-107, @janniklasrose

/bundle/ - needs approval

Files: bundle/scripts/scripts.go, bundle/scripts/scripts_test.go
Suggested: @andrewnester
Also eligible: @pietern, @lennartkats-db, @shreyas-goenka, @anton-107, @janniklasrose

General files (require maintainer)

Files: NEXT_CHANGELOG.md
Based on git history:

• @andrewnester -- recent work in ./

_{Any maintainer (@andrewnester, @anton-107, @pietern, @shreyas-goenka, @simonfaltum, @renaudhartert-db) can approve all areas.
See OWNERS for ownership rules.}