pulsar: add \GF macro, rename corona2024->boschini2024corona, bump Go to 1.26.3

- spec/pulsar-m.tex: define \newcommand{\GF}{\mathrm{GF}} so any later
    GF(q)/GF(2^k) usage doesn't trip an undefined control sequence.
  - spec/references.bib: rename the Corona bibtex key from corona2024
    to boschini2024corona — matches the catalogue-wide Corona->Corona
    rename (Corona is the production name).
  - go.mod: go directive 1.22.0 -> 1.26.3 (matches the rest of the stack).

go.mod

@@ -1,6 +1,6 @@
 module github.com/luxfi/pulsar
 
-go 1.22.0
+go 1.26.3
 
 require (
 	github.com/cloudflare/circl v1.6.3

spec/pulsar-m.tex

@@ -55,6 +55,7 @@
 \newcommand{\Rq}{R_q}
 \newcommand{\Zq}{\mathbb{Z}_q}
 \newcommand{\Tq}{\mathbb{T}_q}
+\newcommand{\GF}{\mathrm{GF}}
 \newcommand{\negl}{\mathsf{negl}}
 \newcommand{\poly}{\mathsf{poly}}
 \newcommand{\PPT}{\mathsf{PPT}}

spec/references.bib

@@ -5,7 +5,7 @@
 % conference proceedings. Do not paraphrase or guess — every entry has a
 % checked source URL.
 
-@misc{corona2024,
+@misc{boschini2024corona,
   author       = {Cecilia Boschini and Darya Kaviani and Russell W.~F.~Lai
                   and Giulio Malavolta and Akira Takahashi and Mehdi Tibouchi},
   title        = {Corona: Practical Two-Round Threshold Signatures from Learning with Errors},