feat: add function-level slicing mode (--function-slice)

[lsz-asd]

Summary

Add function-level slicing as an alternative to the existing line-level
slicing. When --function-slice (-fs) is enabled, the slicing criterion
is expanded from a single source line to all trace statements within the
containing method, producing a method-grained backward slice.

Motivation

Line-level slicing answers "which lines affect this specific statement?"
Function-level slicing answers "which methods affect this entire function?"
This is useful for understanding inter-procedural dependencies at a higher
level of abstraction.

Changes

File	Change
CommandParser.java	Add -fs/--function-slice CLI flag
Slicer.java	Expand slicing criterion to all statements in the target method
SlicePrettyPrinter.java	New — method-grouped output and DOT graph
slicer4j.py	Add -fs and -tcd flags to Python wrapper

New output files (only with -fs)

• slice-function.log — slice results grouped by method signature
• slice-pretty.log — human-readable report with inter-method dependency graph
• slice-graph-function.pdf — method-level DOT dependency graph

Usage

# Line-level (existing behavior, unchanged)
python3 slicer4j.py -j app.jar -o out/ -b Foo:42 -m "Foo arg1"

# Function-level (new)
python3 slicer4j.py -j app.jar -o out/ -b Foo:42 -m "Foo arg1" -fs

Test plan

• Compiles with mvn -Dmaven.test.skip=true clean package
• Tested on benchmarks/SliceMe — function-level slice correctly groups
  main() and parse() methods
• Tested on benchmarks/JacksonCore_4b — function-level slice captures
  TextBuffer.expandCurrentSegment() dependencies
• Existing test suite unaffected (no regressions)

Screenshots