feat: add C implementation for erlang/logpdf

Add implementation of logpdf for Erlang distribution

Signed-off-by: Kamal Singh Rautela <130351010+rautelaKamal@users.noreply.github.com>

Author: rautelaKamal

lib/node_modules/@stdlib/stats/base/dists/erlang/logpdf/lib/native.js

@@ -0,0 +1,48 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var addon = require( './../src/addon.node' );
+
+
+// MAIN //
+
+/**
+* Evaluates the natural logarithm of the probability density function (PDF) for an Erlang distribution with shape parameter `k` and rate parameter `lambda` at a value `x`.
+*
+* @private
+* @param {number} x - input value
+* @param {NonNegativeInteger} k - shape parameter
+* @param {PositiveNumber} lambda - rate parameter
+* @returns {number} evaluated logPDF
+*
+* @example
+* var y = logpdf( 0.1, 1, 1.0 );
+* // returns ~-0.1
+*/
+function logpdf( x, k, lambda ) {
+	return addon( x, k, lambda );
+}
+
+
+// EXPORTS //
+
+module.exports = logpdf;