fix: nimcheck improvements for generics, JS operators, Python 3.10+ syntax

- Add tolerantMode for generic Nim code with < > brackets
- Fix JS ?. and ?? operator tokenization
- Add Python 3.10 match/case keywords, underscore prefix support
- Fix f-string parsing operator precedence bug
- Fix duplicate foundClosing assignments in JS/PHP tokenizers
- Treat unknown flavors as info instead of error
- Add comprehensive test coverage for all fixes

tests/fixtures/bash/valid.sh

@@ -1,2 +1,5 @@
 #!/usr/bin/env bash
 echo "Hello, world!"
+if [[ "$a" = "$b" ]]; then
+  echo "a equals b"
+fi

tests/fixtures/javascript/valid.js

@@ -1,3 +1,5 @@
 function greet(name) {
   return `Hello, ${name}!`;
 }
+
+const x = obj?.prop ?? 'default';

tests/fixtures/nim/with_generics.nim

@@ -0,0 +1,14 @@
+## Nim code with generics - should validate cleanly (no false "Unclosed '<'")
+proc jarray[T](node: T): T =
+  result = node
+
+proc pair[A, B](a: A, b: B): (A, B) =
+  (a, b)
+
+proc findIf[T](items: seq[T], pred: proc(x: T): bool): Option[T] =
+  for item in items:
+    if pred(item):
+      return some(item)
+
+proc compare[T](a, b: T): bool =
+  a < b and b > a

tests/fixtures/python/valid.py

@@ -1,2 +1,11 @@
 def hello(name: str) -> str:
     return f"Hello, {name}!"
+
+def process(value):
+    match value:
+        case 1:
+            return 'one'
+        case _:
+            return 'other'
+
+_private_var = 42

tests/test_javascript_exhaustive.nim

@@ -144,3 +144,18 @@ suite "JavaScript Exhaustive Tests":
     let src = "const big = 9007199254740991n;\n"
     let result = validateSource(src, flavor = lfJavaScript)
     check result.errors.len >= 0
+
+  test "nullish coalescing operator ?? working":
+    let src = "const x = a ?? b ?? c;\n"
+    let result = validateSource(src, flavor = lfJavaScript)
+    check result.errors.len == 0
+
+  test "optional chaining ?. operator working":
+    let src = "const x = obj?.prop?.nested;\n"
+    let result = validateSource(src, flavor = lfJavaScript)
+    check result.errors.len == 0
+
+  test "combined ?. and ?? operators":
+    let src = "const x = obj?.prop ?? 'default';\n"
+    let result = validateSource(src, flavor = lfJavaScript)
+    check result.errors.len == 0

tests/test_nim_exhaustive.nim

@@ -164,3 +164,38 @@ suite "Nim Exhaustive Tests":
     let src = "proc test() =\n  ##[ this is a doc comment\n  that never ends\n  discard\n"
     let result = validateSource(src, flavor = lfNim)
     check result.errors.len >= 0  # May not detect ##[ unclosed
+
+  test "generic proc with type parameter":
+    let src = "proc jarray[T](node: T): T =\n  result = node\n"
+    let result = validateSource(src, flavor = lfNim)
+    check result.errors.len == 0
+
+  test "generic proc with multiple type params and comparisons":
+    let src = "proc compare[T](a, b: T): bool =\n  a < b and b > a\n"
+    let result = validateSource(src, flavor = lfNim)
+    check result.errors.len == 0
+
+  test "generic proc with Option[T]":
+    let src = "proc findIf[T](items: seq[T], pred: proc(x: T): bool): Option[T] =\n  for item in items:\n    if pred(item):\n      return some(item)\n"
+    let result = validateSource(src, flavor = lfNim)
+    check result.errors.len == 0
+
+  test "template with generics":
+    let src = "template wrap[T](x: T): T = x\n"
+    let result = validateSource(src, flavor = lfNim)
+    check result.errors.len == 0
+
+  test "chained comparisons with < >":
+    let src = "let x = 1 < 2 and 3 > 2 and 4 >= 1 and 5 <= 10\n"
+    let result = validateSource(src, flavor = lfNim)
+    check result.errors.len == 0
+
+  test "valid .nim file with generics":
+    let result = validateFile("tests/fixtures/nim/with_generics.nim")
+    check result.errors.len == 0
+
+  test "tolerant mode with false angle bracket":
+    let opts = newValidationOptions(tolerantMode = true)
+    let src = "proc jarray[T](node: T): T =\n  result = node\n"
+    let result = validateSource(src, flavor = lfNim, options = opts)
+    check result.errors.len == 0

tests/test_python_exhaustive.nim

@@ -149,3 +149,8 @@ suite "Python Exhaustive Tests":
     let src = "s = \"line1\\\nline2\\\nline3\"\n"
     let result = validateSource(src, flavor = lfPython)
     check result.errors.len >= 0
+
+  test "underscore private convention":
+    let src = "_private = 42\n"
+    let result = validateSource(src, flavor = lfPython)
+    check result.errors.len == 0