More minor bugfixes

- make pollcat_loop() work as expected with no structs linked, by
  - calling usleep() instead of poll()
  - refactoring delay calculation and reset into pollcat_time_value()
- simplify pollcat_timer_dispatch() in case of slow callbacks
  - deprecate pollcat_timer_dispatch_thresh
- revise tests/timer.c to support two new options:
  - -s to monitor stdin with pollcat_fd_add()
  - -w to use pollcat_loop() instead of handling main-loop separately
- make pollcat_dump() always present in header, since it's always compiled in
- add Makefile rules for installing tests, for easier running on cross-compiled targets

tests/Makefile

@@ -1,7 +1,7 @@
 # Test stubs Makefile
 #
 # This file is part of the Pollcat Library.
-# Copyright (C) 2022 Expatria Technologies Inc.
+# Copyright (C) 2022,2025 Expatria Technologies Inc.
 # Contact: Morgan Hughes <morgan@expatria.ca>
 #
 # The Pollcat Library is free software: you can redistribute it and/or modify it under the
@@ -18,6 +18,10 @@
 #
 # vim:ts=4:noexpandtab
 
+# Integrators should override these
+PREFIX ?= /usr/local
+export PREFIX DESTDIR
+
 # output targets
 BINS := \
 	poll \
@@ -57,7 +61,8 @@ timer: $(TIMER_OBJS)
 
 
 install:
-	false
+	mkdir -p $(DESTDIR)$(PREFIX)/bin
+	install -m755 $(BINS) $(DESTDIR)$(PREFIX)/bin
 
 clean:
 	rm -f $(POLL_OBJS)