[WIP] Add new string functions

[seladb]

Update existing and add new string functions.

Description

• Update Trim to accept the characters to trim
• Add new string functions: RTrim, LTrim, RPad, LPad, Replace
• Noe: RPad and LPad are not available in SQLite

Motivation and Context

This aligns with what's available in Django

How Has This Been Tested?

• Added tests for existing and new functions

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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_{Comparing seladb:add-string-functions (efc4f5f) with develop (179ea6f)}