chore: add apache license

[robwoodgate]

This licensing scheme provides maximum flexibility for downstream users. Apache 2.0 includes an explicit patent grant and patent retaliation clause, offering additional protection in the event of patent litigation. Under a dual MIT OR Apache-2.0 model, downstream users may choose either license at their discretion.

This brings cashu-ts into alignment with the licensing approach already proposed by Cashu CDK. As Cashu continues to develop as a multi-language ecosystem, with TypeScript an increasingly common implementation language, adopting the same dual MIT OR Apache-2.0 model helps provide consistent flexibility and legal protections across Cashu implementations.

If you're on the below list and agree with this change, please add a comment with:

I hereby re-license my previous contributions to Cashu-TS under [Apache 2.0](https://choosealicense.com/licenses/apache-2.0/) in addition to the existing [MIT](https://choosealicense.com/licenses/mit/) license.

• @a1denvalu3
• @alexlwn123
• @BilligsterUser
• @bordalix
• @callebtc
• @cjbeery24
• @d4rp4t
• @dipunm
• @Egge21M
• @gandlafbtc
• @gudnuf
• @ildella
• @IroncladDev
• @jaas666
• @jbojcic1
• @Kelbie
• @KKA11010
• @KvngMikey
• @minibits-cash
• @nogringo
• @prusnak
• @purrgrammer
• @robwoodgate
• @SDBowen
• @TheRealCheebs
• @thesimplekid
• @vstabile
• @zk-bits

The following are past contributors with no surviving lines of code (or only trivial/non-copyrightable lines). Your consent is requested as a courtesy.

• @capitalist42
• @Dayvvo (one blank line)
• @jgmcalpine
• @misovan
• @mubarak23
• @starbackr-dev (2 lines of CI YAML)
• @yashbhutwala

[robwoodgate]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.53%. Comparing base (2260968) to head (9c7da2a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #629   +/-   ##
=======================================
  Coverage   91.53%   91.53%           
=======================================
  Files          50       50           
  Lines        4525     4525           
  Branches     1125     1125           
=======================================
  Hits         4142     4142           
  Misses        169      169           
  Partials      214      214           

Flag	Coverage Δ
integration	40.77% <ø> (ø)

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[thesimplekid]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[KvngMikey]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[bordalix]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[jaas666]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[KKA11010]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[Kelbie]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[zk-bits]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[IroncladDev]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[minibits-cash]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[dipunm]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[jbojcic1]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[SDBowen]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[ildella]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[purrgrammer]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[prusnak]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[d4rp4t]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[a1denvalu3]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[BilligsterUser]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[nogringo]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[gudnuf]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[TheRealCheebs]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[gandlafbtc]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.

[Egge21M]

I hereby re-license my previous contributions to Cashu-TS under Apache 2.0 in addition to the existing MIT license.