Add upper and lower bound in BST

[sak-codes]

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[codecov[bot]]

Codecov Report

Merging #537 (e7ea81a) into main (c7b2af7) will increase coverage by 0.005%. The diff coverage is 100.000%.

:exclamation: Current head e7ea81a differs from pull request most recent head d187a40. Consider uploading reports for the commit d187a40 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #537 +/- ## ============================================= + Coverage 98.586% 98.591% +0.005% ============================================= Files 32 32 Lines 4173 4190 +17 ============================================= + Hits 4114 4131 +17 Misses 59 59 ``` | [Impacted Files](https://app.codecov.io/gh/codezonediitj/pydatastructs/pull/537?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=codezonediitj) | Coverage Δ | | |---|---|---| | [pydatastructs/trees/binary\_trees.py](https://app.codecov.io/gh/codezonediitj/pydatastructs/pull/537?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=codezonediitj#diff-cHlkYXRhc3RydWN0cy90cmVlcy9iaW5hcnlfdHJlZXMucHk=) | `97.865% <100.000%> (+0.039%)` | :arrow_up: | [](https://app.codecov.io/gh/codezonediitj/pydatastructs/pull/537?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=codezonediitj)

[sak-codes]

@czgdp1807 Can you please review? It will be used in Multiset implementation in future PR.