fix: handle json.Number in parseInt, parseFloat, and parseUint

[toller892]

Problem

The parseInt, parseFloat, and parseUint template functions only accepted string arguments. When JSON data is parsed with json.Decoder.UseNumber() (or returned from Vault with numeric values), numeric values become json.Number — a named string type that Go's template engine cannot auto-convert to string.

This means templates like {{ .Data.ttl | parseInt }} fail when the value comes from a source that uses json.Number.

Fix

Changed the function signatures from func(s string) to func(s interface{}) with type switches that handle both string and json.Number inputs. Unsupported types return a clear error message.

Testing

• All existing tests pass (template integration tests for parseInt, parseFloat, parseUint)
• Added 20 new unit tests covering json.Number inputs, empty strings, invalid values, and unsupported types
• go vet and goimports clean

Fixes #1584

[hashicorp-cla-app]

Thank you for your submission! We require that all contributors sign our Contributor License Agreement ("CLA") before we can accept the contribution. Read and sign the agreement

Learn more about why HashiCorp requires a CLA and what the CLA includes

---

toller892 seems not to be a GitHub user.
You need a GitHub account to be able to sign the CLA.
If you have already a GitHub account, please add the email address used for this commit to your account.

_{Have you signed the CLA already but the status is still pending? Recheck it.}

[hashicorp-cla-app]

Thank you for your submission! We require that all contributors sign our Contributor License Agreement ("CLA") before we can accept the contribution. Read and sign the agreement

Learn more about why HashiCorp requires a CLA and what the CLA includes

---

toller892 seems not to be a GitHub user.
You need a GitHub account to be able to sign the CLA.
If you have already a GitHub account, please add the email address used for this commit to your account.

_{Have you signed the CLA already but the status is still pending? Recheck it.}