minor issues

[HJLebbink]

Some minor issues that came up while writing docs

[Copilot]

Pull Request Overview

This PR addresses a series of minor issues, including standardizing remove_object calls, improving error messages and type annotations, and replacing literal numeric constants with defined constants for consistency.

• Updated tests to use consistent reference types (e.g. &object_name) when calling remove_object.
• Added explicit type annotations to header maps and replaced hardcoded ranges with MAX_MULTIPART_COUNT constant in builder functions.
• Removed deprecated error variants and standardized string comparisons in response handling.

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/test_put_object.rs	Standardized remove_object calls and updated response assertions.
tests/test_object_put.rs	Updated remove_object invocation to use &object_name consistently.
tests/test_append_object.rs	Same as above—the remove_object call now passes &object_name.
src/s3/utils.rs	Returned a reference for element name instead of converting to a String.
src/s3/response/put_object.rs	Replaced manual extraction of bucket/object with helper functions.
src/s3/response/*	Added type annotations for headers and improved error message comparisons.
src/s3/error.rs	Removed deprecated error variants and commented code.
src/s3/client/stat_object.rs	Updated function signature to use distinct generic parameters.
src/s3/builders/*.rs	Replaced hardcoded values with MAX_MULTIPART_COUNT and improved error messages.