Fix get_tree_diff for sep

[kayjan]

Description

get_tree_diff can now handle

• sep that are different from default (as mentioned in get_tree_diff unable to handle non-default separators #306)
• sep that contain forbidden symbols, there will be a fallback sep
• sep that is different for tree and other_tree, this will throw error now (might not be backwards compatible)

Testing

Add test cases for all the above

Additional notes

Checklist

I have read through the contributing guidelines and ensured that

• I have added a descriptive title for this pull request.
• I have followed the convention and standards, and my code is checked for style and correctness.
• I have added test cases, and unit tests pass with 100% code coverage.
• I have updated the documentation and code docstrings.

Checklist (for reviewer)

• I have added label (breaking / enhancement / bug / documentation) to this pull request, if applicable.
• I will ensure this change is captured in the CHANGELOG.md file.

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
bigtree	100%	100%	0	✔
bigtree.binarytree	100%	100%	0	✔
bigtree.dag	100%	100%	0	✔
bigtree.node	100%	100%	0	✔
bigtree.tree	100%	100%	0	✔
bigtree.utils	100%	100%	0	✔
Summary	100% (2356 / 2356)	100% (994 / 994)	0	✔

[github-actions]

Benchmark

Benchmark suite	Current: 0dcc7f2	Previous: c1c55a9	Ratio
tests/node/test_node_benchmark.py::test_node_benchmark_width_1_depth_10	15732.93036068191 iter/sec (stddev: 0.000017433646979216072)	14872.442776582864 iter/sec (stddev: 0.000017674911815836655)	0.95
tests/node/test_node_benchmark.py::test_node_benchmark_width_1_depth_100	694.9282158252272 iter/sec (stddev: 0.000006820681302020576)	695.9463110831024 iter/sec (stddev: 0.000020245810648049474)	1.00
tests/node/test_node_benchmark.py::test_node_benchmark_width_1_depth_1000	12.372578035680599 iter/sec (stddev: 0.0030353736622349796)	12.166371635500242 iter/sec (stddev: 0.0038396942615142294)	0.98
tests/node/test_node_benchmark.py::test_node_benchmark_width_2_depth_10	68.16188021221322 iter/sec (stddev: 0.003699244116440926)	69.26692821905407 iter/sec (stddev: 0.0032167182673380483)	1.02
tests/node/test_node_benchmark.py::test_node_benchmark_width_1_depth_10_no_assertions	21844.172410059597 iter/sec (stddev: 0.0000012602057026830497)	21455.98144503469 iter/sec (stddev: 6.844086526104986e-7)	0.98
tests/node/test_node_benchmark.py::test_node_benchmark_width_1_depth_100_no_assertions	1544.5254642430448 iter/sec (stddev: 0.000100678782742315)	1667.7281756503478 iter/sec (stddev: 0.00005540393762879646)	1.08
tests/node/test_node_benchmark.py::test_node_benchmark_width_1_depth_1000_no_assertions	112.5687139833065 iter/sec (stddev: 0.003758679623381361)	109.12564160011736 iter/sec (stddev: 0.003989757664698673)	0.97
tests/node/test_node_benchmark.py::test_node_benchmark_width_2_depth_10_no_assertions	91.91239111248214 iter/sec (stddev: 0.003509221543364949)	95.41012286996879 iter/sec (stddev: 0.0028603633903862766)	1.04

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