*: add "noexcept" to many, many function prototypes

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

src/filter/FilterRegistry.cxx

@@ -32,7 +32,7 @@ static const FilterPlugin *const filter_plugins[] = {
 };
 
 const FilterPlugin *
-filter_plugin_by_name(const char *name)
+filter_plugin_by_name(const char *name) noexcept
 {
 	for (unsigned i = 0; filter_plugins[i] != nullptr; ++i)
 		if (strcmp(filter_plugins[i]->name, name) == 0)

src/filter/FilterRegistry.hxx

@@ -39,6 +39,6 @@ extern const FilterPlugin volume_filter_plugin;
 
 gcc_pure
 const FilterPlugin *
-filter_plugin_by_name(const char *name);
+filter_plugin_by_name(const char *name) noexcept;
 
 #endif