Add lookup-table unit tests for activation tables and getValue

Closes a high-leverage coverage gap: every fixed-point activation in the
library reads from precomputed sigmoid/tanh/exp/log/sin/cos tables, but
none of them were directly tested. New suite has three layers:

- Branch coverage on LookupTable<Q>::getValue (clamp lo/hi, knot match,
  flat-region short-circuit, linear interpolation).
- Bit-exact verification that each table entry matches the generator
  output for Q8.8 and Q16.16 across all six functions, catching silent
  corruption of lookupTables.cpp.
- Structural invariants (monotonicity, range, sigmoid complement, tanh
  antisymmetry, sin oddness, cos evenness, endpoint values) and an
  end-to-end accuracy sweep against std:: math with tolerances derived
  from the LSB plus the linear-interpolation chord-error bound.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: danmcleran

Makefile

@@ -5,6 +5,7 @@ check :
 	cd unit_test/nn && make clean && make && make run && cd -
 	cd unit_test/qformat && make clean && make && make run && cd -
 	cd unit_test/qlearn && make clean && make && make run && cd -
+	cd unit_test/lookuptable && make clean && make && make run && cd -
 	cd examples/xor && make clean && make && make release && cd -
 	cd examples/maze && make clean && make && make release && cd -
 	cd examples/dqn_maze && make clean && make && make release && cd -

unit_test/lookuptable/Makefile

@@ -0,0 +1,26 @@
+# Simple Makefile for the lookup-table unit tests.
+# Compiles cpp/lookupTables.cpp with TINYMIND_USE_* macros enabling every
+# (function, Q-format) pair the test exercises.
+MKDIR=mkdir -p ./output
+CC=g++
+WARN=-Wall -Wextra -Werror -Wpedantic
+SOURCES=lookuptable_unit_test.cpp ../../cpp/lookupTables.cpp
+DEFINES=-DTINYMIND_ENABLE_OSTREAMS=1 \
+        -DTINYMIND_USE_SIGMOID_8_8=1 -DTINYMIND_USE_SIGMOID_16_16=1 \
+        -DTINYMIND_USE_TANH_8_8=1 -DTINYMIND_USE_TANH_16_16=1 \
+        -DTINYMIND_USE_EXP_8_8=1 -DTINYMIND_USE_EXP_16_16=1 \
+        -DTINYMIND_USE_LOG_8_8=1 -DTINYMIND_USE_LOG_16_16=1 \
+        -DTINYMIND_USE_SIN_8_8=1 -DTINYMIND_USE_SIN_16_16=1 \
+        -DTINYMIND_USE_COS_8_8=1 -DTINYMIND_USE_COS_16_16=1
+INCLUDES=-I../../include -I../../cpp -I${BOOST_HOME}
+OUT=./output/lookuptable_unit_test
+
+lookuptable_unit_test:
+	$(MKDIR)
+	$(CC) -g $(WARN) -o $(OUT) $(SOURCES) $(DEFINES) $(INCLUDES)
+
+run:
+	cd ./output && ./lookuptable_unit_test && cd ../
+
+clean:
+	rm -f ./output/*