Generate _qualified_ imports to avoid clashes with user code

[andreasabel]

Commits:

• Drop code generation for GHCs < 6.4 (removing some #ifs)
• Qualified import of GHC.Exts in generated code
• Qualified import of Debug.Trace in generated code
• Qualified import of Data.Array in generated code
• Bump to v3.5.1.0; CHANGELOG; update CI to GHC 9.8.2

Fixes #258

• 258

This could be released as 3.5.1.0 (minor bump), assuming that no one uses a contemporary alex to generate code for compilation with GHC 6.2 or lower.

Candidate: https://hackage.haskell.org/package/alex-3.5.1.0/candidate