perf(linter): reduce no-duplicate-case allocations (#28477)

Use smallvec for storing previous case expressions to avoid frequent
heap allocs.

On local fixtures:



Metric | Before → After
-- | --
Allocations | 284 → 63 (−77.8%)
Reallocations | 242 → 36 (−85.1%)
Allocated bytes | 24,096 → 14,464 (−40.0%)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

crates/oxc_linter/src/rules/eslint/no_duplicate_case.rs

@@ -2,6 +2,7 @@ use oxc_ast::ast::Expression;
 use oxc_diagnostics::OxcDiagnostic;
 use oxc_macros::declare_oxc_lint;
 use oxc_span::{ContentEq, GetSpan, Span};
+use smallvec::SmallVec;
 
 use crate::{AstNode, context::LintContext, rule::Rule};
 
@@ -85,7 +86,7 @@ declare_oxc_lint!(
 impl Rule for NoDuplicateCase {
     fn run<'a>(&self, node: &AstNode<'a>, ctx: &LintContext<'a>) {
         let Some(ss) = node.kind().as_switch_statement() else { return };
-        let mut previous_tests: Vec<&Expression<'_>> = vec![];
+        let mut previous_tests: SmallVec<[&Expression<'_>; 8]> = SmallVec::new();
         for test in ss.cases.iter().filter_map(|c| c.test.as_ref()) {
             let test = test.without_parentheses();
             if let Some(prev) = previous_tests.iter().find(|t| t.content_eq(test)) {