Add wrong-t checker for incorrect testing.T usage in testify assertions

[mmorel-35]

Two related misuse patterns cause silent test failures or panics at runtime: passing nil/freshly-created *testing.T to package-level assertions, and using an *Assertions object bound to a parent t inside a t.Run subtest where t is shadowed by a fresh child *testing.T.

New checker: wrong-t (enabled by default, no autofix)

Case 1 — nil or fresh *testing.T as the t argument

// ❌ causes nil-deref panic or misattributed failures
assert.Equal(nil, expected, actual)

u := &testing.T{}
assert.Equal(u, expected, actual)   // variable form also caught

assert.Equal(&testing.T{}, expected, actual)
assert.NoError(new(testing.T), err)

// ✅
assert.Equal(t, expected, actual)

Detected by inspecting the first parameter type of the called function's signature (assert.TestingT / require.TestingT) and checking whether the supplied argument is nil, a composite literal of testing.T, a new(testing.T) call, or a variable declared from one of those expressions.

Case 2 — *Assertions object created with outer t used in a subtest

// ❌ 'a' is bound to the parent t; failures are reported against the wrong test
a := assert.New(t)
t.Run("subtest", func(t *testing.T) {
    a.Equal(expected, actual)
})

// ✅
t.Run("subtest", func(t *testing.T) {
    a := assert.New(t)
    a.Equal(expected, actual)
})

Detected by collecting all := assignments from assert.New/require.New, then for each t.Run callback (with a *testing.T parameter) walking its direct body — stopping at nested function literals to avoid double-reporting — and flagging any receiver whose declaration precedes the callback.

Files

• internal/checkers/wrong_t.go — checker implementation (AdvancedChecker)
• internal/checkers/checkers_registry.go — registration (enabled by default)
• internal/checkers/checkers_registry_test.go, analyzer/checkers_factory_test.go — updated expected lists
• internal/testgen/gen_wrong_t.go, internal/testgen/main.go — test-data generator
• analyzer/testdata/src/checkers-default/wrong-t/ — generated test data
• README.md — checker documentation

Closes #255
Closes #197