Fix: URI path element replace issue due to elements name overlap

[wty-Bryant]

Issue #, if available:
fixes #552

Description of changes:
Old serialization code only indexes first occurrence of target element with left bracket (e.g. {key) without considering common prefix cases like {key1111} and {key}. this pr fixes that by directly searching index of the whole element with the format of {element} or {element+}

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[Madrigal]

Old serialization code only indexes first occurrence of target element via prefix without considering duplication cases,

true, but to expand on it. The old code only looked for {key instead of {key} (unsure if optimization or off-by-one error on original implementation). Because of this, {name and {namespace} both matched {name}

[lucix-aws]

Can we add an error test case? e.g. path is /{bucket}/{key+}, try to replace key buck with some value, expect error