feat: 导入 NMEA-0183 GPS 协议解析库（node-nmea）

NMEA-0183 语句解析器，含 21 个语句类型 codec 与配套单元测试。

- codecs/：APB/BWC/DBT/GGA/GLL/GRMT/GSA/GSV/HDG/HDM/HDT/MWV/RDID/
  RMB/RMC/ROT/RSA/TXT/VTG/VWR/ZDA
- test/：各 codec 对应的 mocha 用例
- .github/workflows/：node与 npm-publish 流水线

许可证：MIT（原作者 James Penn）

codecs/GSA.js

@@ -0,0 +1,44 @@
+/*
+   === GSA - GPS DOP and active satellites ===
+   
+   This is one of the sentences commonly emitted by GPS units.
+
+   ------------------------------------------------------------------------------
+           1 2 3 4                      14 15  16  17  18
+           | | | |                       |  |   |   |   |
+    $--GSA,a,a,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x.x,x.x,x.x*hh
+   ------------------------------------------------------------------------------
+
+   Field Number:
+
+    1) Selection mode
+    2) Mode
+    3) ID of 1st satellite used for fix
+    4) ID of 2nd satellite used for fix
+    ...
+   14) ID of 12th satellite used for fix
+   15) PDOP in meters
+   16) HDOP in meters
+   17) VDOP in meters
+   18) Checksum
+*/
+exports.TYPE = 'active-satellites';
+exports.ID = 'GSA';
+
+exports.decode = function(fields) {
+  // $GPGSA,A,3,12,05,25,29,,,,,,,,,9.4,7.6,5.6
+  var sats = [];
+  for (var i=1; i < 13; i++) {
+    if (fields[i+2]) sats.push(+fields[i+2]);
+  };
+  return {
+    sentence: exports.ID,
+    type: exports.TYPE,
+    selectionMode: fields[1],
+    mode: +fields[2],
+    satellites: sats,
+    PDOP: +fields[15],
+    HDOP: +fields[16],
+    VDOP: +fields[17]
+  };
+}