fix: standardize stratified_sampler dist to uppercase and add verbose…

[danmcgraw94]

Summary

Closes #5.

Addresses the documentation inconsistency Sadie flagged in stratified_sampler(): Usage showed dist = "ev1" while Arguments described "EV1", "Normal", "Uniform". The function internally dispatches on tolower(dist), so both casings already worked — but the docs didn't make that clear.

Changes

• Standardized documentation to use uppercase canonical names ("EV1", "Normal", "Uniform"), matching rfa_simulate()'s convention
• Changed the default argument value from "ev1" to "EV1" so the signature matches the documentation
• Added Case-insensitive note to the @param dist description to acknowledge the existing tolerance
• Added optional verbose argument (default FALSE). When TRUE, emits a cli::cli_inform() message summarizing the stratification on completion

Testing

• R CMD check passes with 0 errors, 0 warnings, 0 notes
• Verified case tolerance by calling with "ev1", "EV1", "Normal", and an invalid value
• No impact on rfa_simulate() — verbose defaults to FALSE, and the internal tolower() dispatch was already present