fix: skip Kotlin operator convention imports in unused-import detection

[ariancovac]

Problem

Kotlin invokes convention (operator) functions implicitly by the compiler. The clearest case: import androidx.compose.runtime.getValue / setValue are required for Compose State/MutableState property delegation (val x by someState, var y by mutableStateOf(...)), yet the names never appear in the file text.

Textual unused-import detection cross-references the imported name against the file body, so it flagged these live imports as unused on every scan (in one real Compose project: 26 findings across 15 files). Removing them breaks compilation — the reviewer either "fixes" a false positive into a build break, or has to dismiss the same findings after every rescan.

Fix

• Add an optional implicit_import_names: frozenset[str] field to TreeSitterLangSpec: names a language invokes implicitly by convention, which a textual reference search cannot rule out.
• Populate it for KOTLIN_SPEC with the Kotlin convention-function table: property delegation (getValue, setValue, provideDelegate), unary/arithmetic/ranges, augmented assignments, containment/indexing/invocation/comparison (contains, get, set, invoke, compareTo, equals), iteration (iterator, next, hasNext), and infix bitwise (and, or, xor, shl, shr, ushr).
• detect_unused_imports skips imported names present in that set. This trades a small amount of recall (a genuinely unused operator-named import goes unreported) for eliminating a false-positive class that directly invites build-breaking fixes — consistent with the detector's conservative stance elsewhere (e.g. skipping errorful parses).
• Other languages are unaffected (the field defaults to empty).

Test

test_unused_imports_skip_implicit_convention_names: with an implicit_import_names-carrying spec, an unreferenced getValue import yields no findings; with a plain spec it is still flagged. Suite: 29 passed in test_treesitter_analysis_direct.py + test_phase_builders.py.