Fix minor build errors, such as unnecessary copies from range enumeration.

[r12f]

Problem

When building on ubuntu 22.04 with gcc 11.3, I am hitting a few minor errors during build: copies from for range enumeration and uninitialized variable before use.

More details are attached as below:

For range enumerations

common/events.cpp: In member function ‘int EventSubscriber::init(bool, int, const event_subscribe_sources_t*)’:
common/events.cpp:368:25: error: loop variable ‘e’ creates a copy from type ‘const std::__cxx11::basic_string<char>’ [-Werror=range-loop-construct]
  368 |         for (const auto e: *subs_sources) {
      |                         ^
common/events.cpp:368:25: note: use reference type to prevent copying
  368 |         for (const auto e: *subs_sources) {
      |                         ^
      |                         &

tests/events_ut.cpp: In function ‘std::string parse_read_evt(std::string&, internal_event_t&, std::string&, sequence_t&, std::string&, event_params_t&)’:
tests/events_ut.cpp:140:21: error: loop variable ‘e’ creates a copy from type ‘const std::pair<const std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char> >’ [-Werror=range-loop-construct]
  140 |     for (const auto e: evt) {
      |                     ^
tests/events_ut.cpp:140:21: note: use reference type to prevent copying
  140 |     for (const auto e: evt) {
      |                     ^
      |                     &

Uninitialized variable

tests/stringutility_ut.cpp: In member function ‘virtual void STRINGUTILITY_hex_to_binary_Test::TestBody()’:
tests/stringutility_ut.cpp:79:36: error: ‘a’ may be used uninitialized [-Werror=maybe-uninitialized]
   79 |     EXPECT_TRUE(swss::hex_to_binary("01020aff05", a.data(), a.size()));
      |                 ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/11/tuple:39,
                 from /usr/include/c++/11/bits/stl_map.h:63,
                 from /usr/include/c++/11/map:61,
                 from ./common/logger.h:6,
                 from ./common/stringutility.h:3,
                 from tests/stringutility_ut.cpp:1:
/usr/include/c++/11/array:176:7: note: by argument 1 of type ‘const std::array<unsigned char, 5>*’ to ‘constexpr std::array<_Tp, _Nm>::size_type std::array<_Tp, _Nm>::size() const [with _Tp = unsigned char; long unsigned int _Nm = 5]’ declared here
  176 |       size() const noexcept { return _Nm; }
      |       ^~~~
tests/stringutility_ut.cpp:77:33: note: ‘a’ declared here
   77 |     std::array<std::uint8_t, 5> a;
      |                                 ^

Fix

Changed range from value to reference as compiler suggested and initialized the uninitialized array as 0.

[bingwang-ms]

@prsunny Please help review this change. Thanks!

[prsunny]

lgtm

[qiluo-msft]

events_init_subscriber

You do not mention the reason of this change anywhere. Seems like it is not necessary.

[qiluo-msft]

As comment