fix(eliminate): preserve inline comments and blank lines via span-based text patching

[NikolaRHristov]

Fixes the root cause of the formatting regression: inline comments and blank lines being dropped whenever any elimination occurred.

Problem

Transform::Run called prettyplease::unparse(&Ast) on the entire syn::File whenever any binding was eliminated. prettyplease only sees the AST; it has no view of // inline comments, blank lines, or original spacing. Every touched file was reprinted in prettyplease canonical style, altering regions of the file that had nothing to do with the eliminated bindings.

Fix

New: Transform/Patch.rs

Provides three primitives:

• LineColToByte(source, line, col) - converts 1-based line / 0-based col (proc_macro2 convention) to a byte offset in the source string.
• SpanBytes(span, source) - extracts (start, end) byte offsets from a proc_macro2::Span. Returns None when span-location data is absent (triggers fallback).
• StmtLineRange(stmt, source) - returns the full line range of a statement including leading indent and trailing newline, so deletion leaves no blank lines.
• ApplyPatches(source, patches) - applies a sorted non-overlapping slice of Patch structs (byte-range replacements) against the source string. Returns None on overlap or out-of-bounds.

Changed: Transform/mod.rs

Run now calls TryPatchSource(source, mutated_ast) after elimination:

1. Re-parses Source into OriginalAst whose Spans are anchored to Source bytes.
2. Walks OriginalAst and MutatedAst in parallel over function items.
3. CollectBlockPatches aligns statements between original and mutated blocks by token-stream equality. Statements present in the original but absent in the mutated block are emitted as delete patches. Statements that are present in both but have different token text (substituted identifier) are emitted as replace patches.
4. Patches are sorted by start offset and passed to ApplyPatches.
5. If any span resolution returns None, TryPatchSource returns None and Run falls back to prettyplease::unparse - behaviour is never worse than before.

Tests added

In Patch::Tests:

• ApplyNoPatches - identity case
• ApplySingleDelete - range delete
• ApplySingleReplace - range replace
• ApplyTwoPatches - two disjoint patches
• OverlappingPatchesReturnNone - overlap guard
• OutOfBoundsPatchReturnsNone - bounds guard
• LineColToByteFirstLine / LineColToByteSecondLine / LineColToByteOutOfRange