#215 backlash error

[Weisl]

Problem
Renaming objects would intermittently crash with:

re.error: bad escape \T at position 13
This happened because re.sub() treats its replacement string as a template where backslashes carry special meaning (\1 = group 1, \n = newline, etc.). If any replacement value contained a backslash followed by a letter — e.g. a Windows file path from @f, or a user-defined string variable — Python's regex engine would raise an error rather than insert the text literally. This only affected certain objects/scenes because the crash depended on what the variable values resolved to at runtime.

Changes
variable_replacer/variable_replacer.py
All re.sub() calls in replaceInputString now pass the replacement as a lambda callable instead of a bare string. When re.sub receives a callable, it calls it with the match object and uses the return value verbatim — no template processing, no backslash interpretation. This is the root cause fix.

operators/search_replace.py

Non-regex, case-insensitive path: same lambda fix applied to replaceSearch.sub(...).
Regex mode path: replaced the bare re.sub(searchReplaced, replaceReplaced, ...) call with explicit re.compile + pattern.sub, wrapped in try/except re.error blocks. Invalid regex patterns or replacement strings now surface a proper error popup instead of a raw traceback. The regex mode replacement is intentionally kept as a string (not a lambda) so users can still use backreferences like \1 in their regex replacements.
operators/search_select.py
The case-insensitive re.search call is now wrapped in try/except re.error, so an invalid search expression shows an error popup instead of crashing.