feat(params): accept --limitGenomeGenerateRAM for STAR CLI compatibility

[pinin4fjords]

Summary

Accepts the STAR-compatible --limitGenomeGenerateRAM flag at the CLI parser. The value is parsed and stored but not currently enforced — rustar's memory management is independent. This unblocks every wrapper that passes the flag derived from job resources (e.g. nf-core/rnaseq's STAR_GENOMEGENERATE Nextflow module).

Before

$ rustar-aligner --runMode genomeGenerate --limitGenomeGenerateRAM 31000000000 ...
error: unexpected argument '--limitGenomeGenerateRAM' found

After

$ rustar-aligner --runMode genomeGenerate --limitGenomeGenerateRAM 31000000000 ...
(proceeds; flag value accepted but not enforced)

Test plan

• cargo build
• cargo clippy --all-targets -- -D warnings
• cargo fmt --check
• cargo test --lib
• Smoke test confirms flag is no longer rejected at the CLI parser.

A future PR can wire the value into the suffix-array build path if real RAM capping is desired.

Fixes #25

[pinin4fjords]

Verified the fix end-to-end on macos/aarch64 with the binary built from b8ba281:

$ ./target/debug/rustar-aligner --runMode genomeGenerate --limitGenomeGenerateRAM 31000000000 \
    --genomeDir /tmp/rgg-test --genomeFastaFiles /dev/null
[INFO  rustar_aligner] rustar-aligner 0.1.0
[INFO  rustar_aligner] runMode: genomeGenerate
[INFO  rustar_aligner] runThreadN: 1
[INFO  rustar_aligner] genomeDir: /tmp/rgg-test
[INFO  rustar_aligner] genomeFastaFiles: ["/dev/null"]
[INFO  rustar_aligner] Building genome index...
[INFO  rustar_aligner::index] Loading FASTA files...
Error: FASTA parsing error: no chromosomes found in FASTA files

No "unexpected argument" — flag is parsed cleanly and the run proceeds to the FASTA-loading stage as expected. The matching error from the pre-fix binary was:

error: unexpected argument '--limitGenomeGenerateRAM' found
  tip: a similar argument exists: '--limitBAMsortRAM'

So #25's reproducer no longer fires. LGTM from the consumer side.

[pinin4fjords]

I'm unsure to what extent this makes sense really. I get Claude's rationale that it would be good not to break any CLI options though, even if they do nothing.

[pinin4fjords]

Added a runtime warning when the flag is set to a non-default value. Verified on macOS/aarch64:

$ ./target/debug/rustar-aligner --runMode genomeGenerate --limitGenomeGenerateRAM 8000000000 ...
[WARN  rustar_aligner] --limitGenomeGenerateRAM 8000000000 accepted but not enforced; rustar manages genome-generation memory independently
Error: FASTA parsing error: no chromosomes found in FASTA files

Default and no-flag invocations stay silent (no spurious warning when the user didn't explicitly ask for a cap). A user passing a real RAM cap now sees that the cap isn't applied rather than having to read the PR body to find out.

Pushed as a follow-up commit (cc3e48a) on the same branch.