fix: patch Huffman OOB read and optimize encoders

[LessUp]

Summary

• Security fix: Patch out-of-bounds read in Huffman decode table build. When a corrupt or single-child tree caused cur < 0, the e.next = cur assignment at loop exit overwrote the earlier e.next = root safety reset, producing a negative node index. On crafted input with a single-symbol frequency table (e.g. empty input), this led to table[-1] access (undefined behavior). Now guarded with a corrupt flag.
• Optimization: Eliminate O(n) payload copy in arithmetic decode. BitReader now accepts (const uint8_t*, size_t) in addition to const vector&, letting the decoder read directly from the input buffer at the payload offset.
• Optimization: Add reserve() to arithmetic and RLE encoders to reduce reallocation overhead.
• Test coverage: Add all_same_byte.bin corpus file (4096 zero bytes) to exercise RLE single-run and Huffman single-symbol edge cases.

Test plan

• make build — CMake build succeeds with -Wall -Wextra -Werror
• make test — ctest lifecycle tests + CLI smoke (36 checks) all pass
• make lint — clang-format dry-run passes
• New all_same_byte.bin round-trips through all 4 algorithms

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